BACEBeavers in England

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New book by Derek Gow published in September 2020:

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Articles and Reports

2020

Abstract: When planning conservation and reintroductions of native species and control of invasive species, it is important to understand the environmental factors affecting species distributions. Habitat suitability largely determines where species can occur, but in addition to habitat and food resources, it is important to also consider human disturbance and climate when mapping possible distributions. We studied the environmental factors affecting the present distribution of the native Eurasian beaver (Castor fiber) and the invasive North American beaver (C. canadensis) in Finland. We compared the role of food resources, aquatic habitat type, anthropogenic disturbance and climate for beaver occurrence with species distribution models. We created maps of suitable areas for the two species and compared how the results would change if these two ecologically similar species were modelled together. We found that aquatic habitat type and climate largely explain the present distributions of the species. In addition, there were differences between the species in their preference for food resources, aspen, birch and grey alder. However, we suspect that the species’ reintroduction history, i.e. the differences in the present environment, much explain the differences found between the species. We conclude that when planning possible reintroductions for the Eurasian beaver, factors other than food resources should also be considered. We also suggest that studies on habitat suitability should consider the history of the species and include data from different environments. Thus, more comprehensive information for management planning would be achieved and a better ability to predict the location of optimal areas for the species.

Abstract: Species introductions threaten ecosystem function worldwide, and interactions among introduced species may amplify their impacts. Effects of multiple invasions are still poorly studied, and often, the mechanisms underlying potential interactions among invaders are unknown. Despite being a remote and well-conserved area, the southern portion of South America has been greatly impacted by invasions of both the American beaver (Castor canadensis) and Brown Trout (Salmo trutta fario). Here, we compared growth, condition, diet, and stable isotopes of sulfur δ34S, nitrogen δ15N, and carbon δ13C for stream-living Brown Trout from streams with (n = 6) and without (n = 6) beaver in Tierra del Fuego, Chile. We show that beaver may facilitate the success of trout by positively influencing fish growth. Beaver indirectly provide greater food subsidies (i.e., macroinvertebrate abundances) by modifying the local aquatic environment through active dam and lodge building suggesting a one-way positive interaction. Trout in beaver-influenced streams occupied a slightly higher trophic level with more depleted sulfur and carbon isotopic ratios suggesting that food web pathways rely on secondary production from autochthonous origin. Trout in beaver-influenced streams had a wider dietary breadth with diptera and amphipoda as the prey items providing most of the energy, whereas in streams without beaver, trichoptera were the main source of energy for trout. Ultimately, we find that these two species, which have never co-occurred naturally, bring about the same ecosystem function and the beneficial influences in their native ranges as in invaded systems.

International Union for the Conservation of Nature (IUCN) guidelines state that anticipated impacts must be considered in wildlife reintroduction, including theimpacts on humans. Further, since reintroduction projects can be halted by resulting human–wildlife conflicts or human–human conflicts about wildlife, the perceptions of takeholders and publics are of great importance. Eurasian beaver (Castor fiber) reintroduction is being debated in Great Britain at a devolved level. A decision has already been taken in Scotland to allow beavers already present to remain, while a number of reintroduction trials are taking place in England (both fenced and unfenced). There are also proposals for a reintroduction trial in Wales. We use a sub‐set of results from a nationwide survey (n = 2,759) to identify four social areas that we propose decision‐makers should consider in the debate: key stakeholder perceptions; engagement methods; attitudes towards legal protection and management responsibilities; and support for management techniques. In this paper, we investigate the complex social dimensions of wildlife reintroduction and we argue that emphasis should be placed on the need to recognise societal perceptions of potential management solutions, beyond perceptions of reintroduction itself. This is paramount in order to develop a management strategy that is more likely to garner social support and reduce potential future conflicts, should beaver reintroduction proceed.

Social factors hold implications for the success or failure of wildlife reintroductions. Potential conflict issues may prevent projects from proceeding or succeeding. The manner in which wildlife managers engage with affected people in conflict scenarios may prevent or contribute toward conflict escalation, so an understanding of how to improve engagement is required. We conducted interviews with individuals who reported conflicts with beavers (Castor fiber) within the case study of a reintroduction trial in England, called the ‘River Otter Beaver Trial’. Using a qualitative thematic analysis, we identified five themes to be considered when engaging with affected people in beaver reintroduction conflicts: (1) Proactive Engagement or a Fast Response; (2) Appropriate Communication; (3) Shared Decision-Making; (4) Sense that Humans are Responsible for Conflicts with Reintroduced Species; (5) A Need for Certainty. We conclude that engagement with affected individuals will likely be improved, with reduced conflict potential, where these themes are addressed.

Wildlife reintroduction projects are required to account for social and economic factors. Wildlife tourism is often cited as a benefit of reintroduction, so an understanding of whether and how this manifests is required. Through a case study of a village in the catchment of a live reintroduction project (Eurasian beaver (Castor fiber) in England) we reveal how reintroduced species tourism has economic benefit for local business, but the scale of benefit is dependent upon business initiatives that take the opportunity (eg merchandise, marketing etc.). We suggest reintroduction practitioners should actively encourage local businesses to maximise opportunities, especially where tourism is cited as a reason to reintroduce. We recommend further research into whether benefits remain in the long-term, but speculate some value will persist. Finally, we recognise reintroduction-related wildlife tourism may interact with other local issues, but seeing a reintroduced species or signs of its activity can produce positive emotional responses.

Social factors hold implications for the success or failure of wildlife reintroductions. Potential conflict issues may prevent projects from proceeding or succeeding. The manner in which wildlife managers engage with affected people in conflict scenarios may prevent or contribute toward conflict escalation, so an understanding of how to improve engagement is required. We conducted interviews with individuals who reported conflicts with beavers (Castor fiber) within the case study of a reintroduction trial in England, called the ?River Otter Beaver Trial?. Using a qualitative thematic analysis, we identified five themes to be considered when engaging with affected people in beaver reintroduction conflicts: (1) Proactive Engagement or a Fast Response; (2) Appropriate Communication; (3) Shared Decision-Making; (4) Sense that Humans are Responsible for Conflicts with Reintroduced Species; (5) A Need for Certainty. We conclude that engagement with affected individuals will likely be improved, with reduced conflict potential, where these themes are addressed.

Abstract: Spatial distribution and habitat selection are integral to the study of animal ecology. Habitat selection may optimize the fitness of individuals. Hutchinsonian niche theory posits the fundamental niche of species would support the persistence or growth of populations. Although niche-based species distribution models (SDMs) and habitat suitability models (HSMs) such as maximum entropy (Maxent) have demonstrated fair to excellent predictive power, few studies have linked the prediction of HSMs to demographic rates. We aimed to test the prediction of Hutchinsonian niche theory that habitat suitability (i.e., likelihood of occurrence) would be positively related to survival of American beaver (Castor canadensis), a North American semi-aquatic, herbivorous, habitat generalist. We also tested the prediction of ideal free distribution that animal fitness, or its surrogate, is independent of habitat suitability at the equilibrium. We estimated beaver monthly survival probability using the Barker model and radio telemetry data collected in northern Alabama, United States from January 2011 to April 2012. A habitat suitability map was generated with Maxent for the entire study site using landscape variables derived from the 2011 National Land Cover Database (30-m resolution). We found an inverse relationship between habitat suitability index and beaver survival, contradicting the predictions of niche theory and ideal free distribution. Furthermore, four landscape variables selected by American beaver did not predict survival. The beaver population on our study site has been established for 20 or more years and, subsequently, may be approaching or have reached the carrying capacity. Maxent-predicted increases in habitat use and subsequent intraspecific competition may have reduced beaver survival. Habitat suitability-fitness relationships may be complex and, in part, contingent upon local animal abundance. Future studies of mechanistic SDMs incorporating local abundance and demographic rates are needed.

Abstract: The aim of this review is to analyze the literature on the impact of beavers on lakes, summarize their effects, describe consequences for biotic and abiotic components, and highlight unresolved issues and perspectives. Beaver activity changes vegetation structure to the greatest extent, indirectly affecting other ecosystem components. Damming of flowing lakes increases the littoral area, which affects diversity and abundance of invertebrates, amphibians, birds, and mammals. Beavers’ alteration of the water regime and heterogeneity and connectivity of habitats has significant effects on zoobenthos, fish, and amphibians. Changes in hydrochemical properties directly affect phytoplankton and benthos. Unlike river ecosystems, where habitats are altered from flowing to still water, in lake ecosystems, habitat type is not usually changed (from lotic to lentic) but their quality (e.g., heterogeneity, connectivity) is. Beaver activity in rivers leads to increased limnophilic biodiversity, but in lakes, it leads to conservation of pre-existing lentic ecosystems. Therefore, impacts of beavers could be of greater importance to limnophilic complexes in lakes than to streams, especially after long time of beaver absence. Digging activity has a more significant role in lakes (especially floodplain) than in rivers. Beaver alteration of heterogeneity and connectivity of habitats is well studied, but not enough is known about impacts on the water regime of seasonally flowing waters, hydrochemical changes (especially eutrophication), amphibian life cycles, phytoplankton and zooplankton communities, parasitocenoses, and coarse woody debris. Methodological difficulties are noted, which are associated with the correct choice of control lakes. Further studies on riverine lakes are crucial. In considerations of climatic changes and anthropogenic impact, beavers may be an additional aid to conserving small lake ecosystems.

Abstract: There is growing interest in developing effective interventions to manage socially and environmentally damaging conservation conflicts. There are a variety of intervention strategies that can be applied in various contexts, but the reasons one type of intervention is chosen over another remain underexplored. We surveyed conservation researchers and practitioners (n = 427) to explore how characteristics of conflicts and characteristics of decision makers influence recommendations to alleviate conservation conflict. Using a full-factorial design, we experimentally manipulated 3 aspects of the descriptions of 8 different wildlife-conflict scenarios (development status of the conflict country, conflict framing, and legality of killing wild animals) and recorded which of 5 intervention types (wildlife impact reduction, awareness, enforcement, economic incentives, or stakeholder engagement) respondents prioritized. We also recorded information on respondents? demographic and disciplinary backgrounds. Stakeholder-based interventions were recommended most often in the survey and in written feedback. However, when we fitted multinomial mixed logit models with fully completed scenario responses (n = 411), recommendations were influenced by small changes in the details of conflict and differed according to respondent characteristics. Enforcement and awareness interventions were prioritized relatively more for conflicts in more highly developed nations and by respondents with more natural science backgrounds and relatively less experience with conflict. Contrastingly, economic interventions were prioritized more when wildlife killing was described as illegal. Age, gender, and development status of the respondent’s home country also predicted some intervention decisions. Further, interrogating the influences shaping conservation decision making will further helps in the development of evidence-informed interventions.Graham, H. A., Puttock, A., Macfarlane, W. W., Wheaton, J. M., Gilbert, J. T., Campbell-Palmer, R., Elliott, M., Gaywood, M. J., Anderson, K. & Brazier, R. E. (2020) Modelling Eurasian beaver foraging habitat and dam suitability, for predicting the location and number of dams throughout catchments in Great Britain. European Journal of Wildlife Research 66(3): 42.Abstract: Eurasian beaver (Castor fiber) populations are expanding across Europe. Depending on location, beaver dams bring multiple benefits and/or require management. Using nationally available data, we developed: a Beaver Forage Index (BFI), identifying beaver foraging habitat, and a Beaver Dam Capacity (BDC) model, classifying suitability of river reaches for dam construction, to estimate location and number of dams at catchment scales. Models were executed across three catchments, in Great Britain (GB), containing beaver. An area of 6747 km2 was analysed for BFI and 16,739 km of stream for BDC. Field surveys identified 258 km of channel containing beaver activity and 89 dams, providing data to test predictions. Models were evaluated using a categorical binomial Bayesian framework to calculate probability of foraging and dam construction. BFI and BDC models successfully categorised the use of reaches for foraging and damming, with higher scoring reaches being preferred. Highest scoring categories were ca. 31 and 79 times more likely to be used than the lowest for foraging and damming respectively. Zero-inflated negative binomial regression showed that modelled dam capacity was significantly related (p = 0.01) to observed damming and was used to predict numbers of dams that may occur. Estimated densities of dams, averaged across each catchment, ranged from 0.4 to 1.6 dams/km, though local densities may be up to 30 dams/km. These models provide fundamental information describing the distribution of beaver foraging habitat, where dams may be constructed and how many may occur. This supports the development of policy and management concerning the reintroduction and recolonisation of beaver.

Abstract Beavers have the ability to modify ecosystems profoundly to meet their ecological needs, with significant associated hydrological, geomorphological, ecological, and societal impacts. To bring together understanding of the role that beavers may play in the management of water resources, freshwater, and terrestrial ecosystems, this article reviews the state-of-the-art scientific understanding of the beaver as the quintessential ecosystem engineer. This review has a European focus but examines key research considering both *Castor fiber,*the Eurasian beaver and Castor canadensis, its North American counterpart. In recent decades species reintroductions across Europe, concurrent with natural expansion of refugia populations has led to the return of C. fiber to much of its European range with recent reviews estimating that the C. fiber population in Europe numbers over 1.5 million individuals. As such, there is an increasing need for understanding of the impacts of beaver in intensively populated and managed, contemporary European landscapes. This review summarizes how beaver impact: (a) ecosystem structure and geomorphology, (b) hydrology and water resources, (c) water quality, (d) freshwater ecology, and (e) humans and society. It concludes by examining future considerations that may need to be resolved as beavers further expand in the northern hemisphere with an emphasis upon the ecosystem services that they can provide and the associated management that will be necessary to maximize the benefits and minimize conflicts.

Abstract: Food storage (caching, hoarding), which is observed in many species of animals, increases food availability during times of food insecurity. Both species of beaver (Eurasian beaver, Castor fiber, and the North American beaver, C. canadensis) living at northern latitudes where food may be scarce during winter are larder-hoarders, constructing a food cache of branches of woody species during autumn. We studied the food caching behavior of the Eurasian beaver in three northern European countries (Sweden, Norway, Lithuania) to provide additional insight into this important behavior. Thirty-seven of fortyseven (79%) active family groups had food caches by mid-November and 41 of 47 (87%) had caches by December. Water depth of caches ranged from 1 to 2.3 m and depths at caches in Sweden were significantly deeper than in either Norway or Lithuania. Construction of caches began as early as late September (week 39/40) in Sweden and Lithuania and by mid-October (week 42) in Norway. We observed plasticity in timing of cache initiation but the majority of active sites in all areas had food caches by the beginning of November (week 45). Declining air temperature and mean minimum temperatures of 0°C or below were associated with cache initiation. Caches in Lithuania were larger than in Sweden and Norway, which may be associated with colder winter temperatures. We did not find any relationship between family size or length of territory occupancy and cache size at our Norway sites where population demographics were available. Our results are generally consistent with other studies of food caching behavior in both species and suggest general similarities as well as behavioral plasticity in this important evolutionary strategy.

Abstract: Founder genetic composition can affect reintroduction success, especially as the number of animals released tends to be small and therefore less genetically diverse than their source populations. Numerous translocations and reinforcements of beavers, Castor fiber, have occurred with little regard to geographic and/or genetic origin. Beaver reintroduction to Britain has been haphazard and currently disjointed populations of varying status exist – from sanctioned wild releases, unlicensed populations and naturalistic enclosed projects. This study investigated the genetic composition of two originally unofficially released beaver populations in Britain – Tayside, east Scotland, and River Otter, Devon, to provide data to support decision on their future management. From both wild populations (n = 34Tayside, n = 9Devon) all were confirmed as Eurasian beaver. The vast majority, origin was likely assignable to Germany and the mixed founder population of Bavaria. Eighty-two percent of the Tayside individuals examined at 275 loci were at least as closely related as first cousins, with pairwise estimates of relatedness at 26 loci indicated that the Devon beavers were more closely related on average. So far there is no evidence to suggest that beavers are failing to adapt to the British environment despite their reduced genetic founder based, however attention to genetic augmentation and longer-term management of genetic diversity should be factored into comprehensive restoration plans for the species across Britain. Many recent reintroductions are relying on serial founder events from an already limited founder base and that is counter to best practice in reintroduction planning.

Abstract: Species reintroductions have become a common conservation tool, but they can be controversial and may generate social conflicts. We examine the social dimension of beaver reintroduction in Scotland to understand the issue, the potential for, and impact of, conflict between groups or individuals with differing views on beavers and reintroductions. Using a literature review and semi-structured interviews, we studied planned and unplanned beaver reintroductions to three contrasting landscapes in Scotland: in Knapdale, the reintroduction was planned and science-led, whereas in Tayside and the Highlands, the reintroductions were accidental and/or illegal. Our results highlight the context dependency and complexity of reintroductions. Nationally, the reintroduction of beavers has not become a conflict. At the local scale, we found the Tayside situation to be a conflict with major consequences on the debate at the national scale. While there were no conflicts in the Highlands and Knapdale, the reintroduction remains controversial. The level of conflict depended on the reintroduction process, relationships between stakeholders and their perspectives on their role in nature, their perceptions of landscapes, and the potential issue of lack of control and uncertainty around reintroductions. Based on these findings, the study outlines lessons learned in terms of management, guidelines and implications for future species reintroductions. We argue that to prevent future conflicts over reintroductions, processes must go beyond addressing the effects of reintroduced species on the environment and people’s perceptions and acceptance of these species. Reintroduction processes require engagement in effective discussions which involve all actual and potential stakeholders to agree on broad and long-term conservation plans at the landscape scale. A free Plain Language Summary can be found within the Supporting Information of this article.

Plain English Summary: Over the last decades, species reintroductions have become a common tool in wildlife conservation. These reintroductions focus on species that are considered to be important from an environmental, social and/or historical perspective but that have disappeared or are scarcely present in a given area. The Eurasian Beaver (Castor fiber) is one such species that has been reintroduced in Europe. Beavers affect their environment in various ways which may be seen as beneficial for the landscapes and for other species by some individuals or stakeholder groups. However, these impacts can also be perceived to impact negatively on human activities such as farming, creating conflicts between people over beaver reintroductions. We studied the Scottish beaver reintroduction which started in 2008. Our purpose was to understand if and how the reintroduction developed into a conservation conflict – that is a conflict between people over a conservation process, and whether social, cultural and conceptual issues were at stake. We focused on three situations in Scotland, where the reintroduction process took place differently: in Knapdale, the reintroduction was planned and scientifically-led, whereas in Tayside and in the Highlands the reintroduction was accidental and/or illegal. Our study, based on a literature review and interviews with stakeholders, revealed that the situation has not yet developed into a conflict at the national scale. At the local scale, however, there was conflict in Tayside, where the reintroduction also occurred within a highly productive agricultural area where the beaver population has since thrived and expanded. Overall, the study showed the conflict was dependent on three main issues: the reintroduction process, relationship issues between stakeholders and broader debates on species reintroductions. Based on these findings, the study outlines lessons learned in terms of management, guidelines and implications for future species reintroductions. With reintroductions becoming more common, our study highlights a number of key issues relating to social dimensions of reintroductions that need to be considered in future reintroduction processes, including stakeholder perspectives on their role in nature, their perceptions of landscapes, and the potential issue of lack of control and uncertainty around reintroductions.

Abstract: Once widespread throughout Eurasia and hunted nearly to extinction, the Eurasian beaver Castor fiber has returned to large parts of its former range, largely through active conservation measures. Beavers can substantially alter small, low order streams and their floodplains through dam construction, burrowing activities and tree felling. Therefore, it is presumed they can significantly influence amphibian distributions, species richness and numbers. We undertook a literature review to compare the available data addressing the effects of beaver dams on amphibians in streams of central temperate and boreal Europe. All 19 amphibian species occurring in the study region were found in beaver ponds, despite their distinctly different habitat requirements. Amphibian species acting as pioneers / early colonisers were under-represented in beaver ponds compared to typical forest species. Open country and ubiquitous species showed intermediate patterns. Beaver ponds in headwater streams often supported the entire spectrum of species occurring in the surrounding landscape, and species numbers in beaver modified headwater streams were comparable to those in floodplains of larger natural rivers. In small headwater streams, beavers tended to be the primary providers of essential habitat for amphibians. In contrast, beaver ponds in the floodplains of larger rivers appeared to have less effect and supported lower average species numbers compared to beaver ponds in headwater streams. We propose that beavers and their habitat creating activities are pivotal determinants of amphibian species richness in the headwater streams, which account for 60–80 % of the water bodies in catchment areas in temperate Europe. By creating habitat for endangered amphibian species, beavers and their ability to modify habitats offer extensive opportunities to implement many aspects of the European Water Framework Directive across the continent and to restore amphibian habitats, contributing to their long-term conservation.

Abstract: Beaver dams are gaining popularity as a low-tech, low-cost strategy to build climate resiliency at the landscape scale. They slow and store water that can be accessed by riparian vegetation during dry periods, effectively protecting riparian ecosystems from droughts. Whether or not this protection extends to wildfire has been discussed anecdotally but has not been examined in a scientific context. We used remotely sensed Normalized Difference Vegetation Index (NDVI) data to compare riparian vegetation greenness in areas with and without beaver damming during wildfire. We include data from five large wildfires of varying burn severity and dominant landcover settings in the western USA in our analysis. We found that beaver-dammed riparian corridors are relatively unaffected by wildfire when compared to similar riparian corridors without beaver damming. On average, the decrease in NDVI during fire in areas without beaver is 3.05 times as large as it is in areas with beaver. However, plant greenness rebounded in the year after wildfire regardless of beaver activity. Thus, we conclude that while beaver activity does not necessarily play a role in riparian vegetation post-fire resilience, it does play a significant role in riparian vegetation fire resistance and refugia creation.

Abstract: Gray wolves are a premier example of how predators can transform ecosystems through trophic cascades. However, whether wolves change ecosystems as drastically as previously suggested has been increasingly questioned. We demonstrate how wolves alter wetland creation and recolonization by killing dispersing beavers. Beavers are ecosystem engineers that generate most wetland creation throughout boreal ecosystems. By studying beaver pond creation and recolonization patterns coupled with wolf predation on beavers, we determined that 84% of newly created and recolonized beaver ponds remained occupied until the fall, whereas 0% of newly created and recolonized ponds remained active after a wolf killed the dispersing beaver that colonized that pond. By affecting where and when beavers engineer ecosystems, wolves alter all of the ecological processes (e.g., water storage, nutrient cycling, and forest succession) that occur due to beaver-created impoundments. Our study demonstrates how predators have an outsized effect on ecosystems when they kill ecosystem engineers.

Eurasian beaver (Castor fiber) populations are expanding across Europe. Depending on location, beaver dams bring multiple benefits and/or require management. Using nationally available data, we developed: a Beaver Forage Index (BFI), identifying beaver foraging habitat, and a Beaver Dam Capacity (BDC) model, classifying suitability of river reaches for dam construction, to estimate location and number of dams at catchment scales. Models were executed across three catchments, in Great Britain (GB), containing beaver. An area of 6747 km2 was analysed for BFI and 16,739 km of stream for BDC. Field surveys identified 258 km of channel containing beaver activity and 89 dams, providing data to test predictions. Models were evaluated using a categorical binomial Bayesian framework to calculate probability of foraging and dam construction. BFI and BDC models successfully categorised the use of reaches for foraging and damming, with higher scoring reaches being preferred. Highest scoring categories were ca. 31 and 79 times more likely to be used than the lowest for foraging and damming respectively. Zero-inflated negative binomial regression showed that modelled dam capacity was significantly related (p = 0.01) to observed damming and was used to predict numbers of dams that may occur. Estimated densities of dams, averaged across each catchment, ranged from 0.4 to 1.6 dams/km, though local densities may be up to 30 dams/km. These models provide fundamental information describing the distribution of beaver foraging habitat, where dams may be constructed and how many may occur. This supports the development of policy and management concerning the reintroduction and recolonisation of beaver.

Halley, D. & Schwab , G. (2020) Eurasian beaver population and distribution: The past, present and future.

Abstract: A century ago, overhunting had reduced Eurasian beaver Castor fiber populations to c. 1200 animals in scattered refugia from France to Mongolia. Reintroductions and natural spread have since restored the species to large areas of its original range. Population has more than tripled since the first modern estimate in 1998; the minimum estimate is now c. 1.5 million. Range expansion 2000?2020 has been rapid, with large extensions in western and south-central Europe, southern Russia, and west and central Siberia. Beavers are now re-established in all countries of their former European range except for Portugal, Italy, and the southern Balkans; they occur broadly across Siberia to Mongolia, with scattered populations father east. About half of the world population lives in Russia. Populations appear to be mature in much of European Russia, Belarus, the Baltic States, and Poland. There is a significant population of North American beaver Castor canadensis in Finland and north-west Russia. Most other 20th-Century introductions of this species have become extinct or been removed. Recent DNA studies have improved understanding of Castor fiber population prehistory and history. Two clades, east and west, are extant; a third ?Danube? clade is extinct. Refugial populations were strongly bottlenecked, with loss of genetic diversity through genetic drift. Future range extension, and large increases in populations and in impacts on freshwater systems, can be expected. Beavers are now recolonising densely populated, intensely modified, low-relief regions, such as England, the Netherlands, Belgium, and north-west Germany. They will become much more common and widespread there in coming decades. As beavers are ecosystem engineers with profound effects on riparian habitats, attention to integrating beaver management into these landscapes using experience gained in other areas ? before the rapid increase in population densities and impacts occurs ? is recommended.

Abstract: Beavers (Castor sp.) are ecosystem engineers that cause significant changes to their physical environment and alter the availability of resources to other species. We studied flood dynamics created by American beaver (C. canadensis K.) in a southern boreal landscape in Finland in 1970–2018. We present for the first time, to our knowledge, a temporally continuous long-term study of beaver-induced flood disturbances starting from the appearance of beaver in the area. During the 49 years, the emergence of new sites flooded by beaver and repeated floods (61% of the sites) formed a dynamic mosaic characterized by clustered patterns of beaver sites. As beaver dispersal proceeded, connectivity of beaver sites increased significantly. The mean flood duration was approximately three years, which highlights the importance of datasets with high-temporal resolution in detecting beaver-induced disturbances. An individual site was often part of the active flood mosaic over several decades, although the duration and the number of repeated floods at different sites varied considerably. Variation of flood-inundated and post-flood phases at individual sites resulted in a cumulative number of unique patches that contribute to environmental heterogeneity in space and time. A disturbance mosaic consisting of patches differing by successional age and flood history is likely to support species richness and abundance of different taxa and facilitate whole species communities. Beavers are thus a suitable means to be used in restoration of riparian habitat due to their strong and dynamic influence on abiotic environment and its biotic consequences.

Abstract: The 1972 Clean Water Act (CWA) provided crucial environmental protections, spurring research and corresponding development of a network of expertise that represents critical human capital in freshwater conservation. We used social network analysis to evaluate collaboration across organizational types and ecosystem focus by examining connections between authors of freshwater assessments published since the CWA. We found that the freshwater assessment network is highly fragmented, with no trend toward centralization. Persistent cohesion around organizational subgroups and minimal bridging ties suggest the network is better positioned for diversification and innovation than for learning and building a strong history of linked expertise. Despite an abundance of research activity from university-affiliated authors, federal agency authors provide a majority of the bonding and bridging capital, and diverse agencies constitute the core network. Together, our results suggest that government agencies currently play a central role in sustaining the network of expertise in freshwater assessment, protection, and conservation.

Abstract: There is concern that expanding beaver (Castor fiber) populations will negatively impact the important economic, recreational and ecological resources of Atlantic salmon (Salmo salar) and sea trout (Salmo trutta) populations in Europe. We studied how beaver dams influenced habitat, food resources, growth and movement of juvenile Atlantic salmon and trout on three paired beaver-dammed and beaver-free (control) tributaries of important salmon rivers in central Norway. Lotic reaches of beaver-dammed and control sites were similar in habitat and benthic prey abundance, and ponds were small (<3,000 m2). Though few juvenile salmonids were detected in ponds, trout and salmon were present in habitats below and above ponds (comprising 9%?31% and 0%?57% of the fish collected respectively). Trout dominated control sites (79%?99%), but the greatest proportion of Atlantic salmon were upstream of beaver ponds (0%?57%). Growth rates were highly variable, with no differences in growth between lotic reaches of beaver-dammed and control sites. The condition and densities of juvenile salmon and trout were similar in lotic reaches of beaver-dammed and control sites, though one beaver-dammed site with fine sediment had very few juvenile salmonids. Beaver dams did not block the movement of juvenile salmonids or their ability to use upstream habitats. However, the degree of repeated movements and the overall proportion of fish moving varied between beaver-dammed and control sites. The small scale of habitat alteration and the fact that fish were able to move past dams makes it unlikely that beaver dams negatively impact the juvenile stage of salmon or trout populations.

Abstract Intraspecific competition plays an important role for territory acquisition and occupancy, in turn affecting individual fitness. Thus, understanding the drivers of intraspecific aggression can increase our understanding of population dynamics. Here, we investigated intraspecific aggression in Eurasian (Castor fiber) and North American (Castor canadensis) beavers that are both monogamous, territorial mammals. Combined, we examined tail scars from >1,000 beavers (>2,000 capture events) as part of two long-term studies in Norway and the USA. We investigated the influence of landscape structure, population density, sex, age, and (for Eurasian beavers only) social status and group size on the number of tail scars caused by conspecifics. The number of tail scars was affected by population density in well-connected landscape types (large lakes and rivers), but not in more isolated areas (ponds), where individuals generally had fewer tail scars. Further, the relationship of population density was not linear. In the North American beaver population occurring in large lakes, intraspecific aggression increased with population density. Conversely, in the saturated Eurasian beaver population, intraspecific aggression was in a negative relationship with population density (except at the highest densities), likely due to inverse density-dependent intruder pressure via dispersers. Our findings emphasize that population density can affect intraspecific aggression depending on landscape structure, which might have important consequences for local patterns of dispersal, mate change, and territory occupancy, all of which can affect population dynamics.

Abstract: Social interactions among individuals play a central role in behavioural ecology and studying cohesion of monogamous pairs is important to understand their social relationships. Here, we tested five hypotheses to investigate patterns of pair cohesion in an obligate monogamous mammal, the Eurasian beaver, Castor fiber. We hypothesized that pair cohesion is related to the spatial structure of the territory, territory defence, resource competition, offspring provisioning and the age difference between pair members. We analysed GPS data of 14 beaver pairs and calculated the distance between pair members, and the proportion of territory and core area overlap. While overall territory size was similar between partners and overlap was high, the distance between pair members was large, averaging 500m, and increased with increasing territory size. Moreover, the proportion of core area overlap was comparatively low and decreased with territory size, also indicating low pair cohesion. Pair members were closest at the beginning and end of their nightly activity periods, suggesting that variation in pair cohesion was caused by the spatial structure of territories with the lodge serving as a central place. We found no support for the other hypotheses, but the overall low pair cohesion might nevertheless serve to increase territory defensibility and reduce intrapair competition for resources. Ultimately, low pair cohesion might be caused by the obligate monogamous mating system of beavers, leading to the defence of spatially structured territories rather than the defence of a partner.

The European beaver (Castor fiber) has extended its range into most Central European countries over the past 30 years, resulting in increased forestry damage and water management issues. As the number of beavers increases populations become established in new types of habitat. In the Czech Republic, for example, established beaver populations are now found on rivers flowing through agricultural landscapes, where living conditions differ significantly to those found in forest landscapes. To date, there have been no studies on the impact of beavers on agricultural production. The aim of this study was (1) to describe how beavers graze field crops, and (2) to estimate potential damage to agricultural production. This 2-year study examined five beaver territories in agricultural landscapes where crops were separated from watercourses by a narrow strip of bank vegetation. Beavers fed on all crop types grown in their territories throughout the growing period (May–October), peaking from mid-June to mid-July. The beavers clearly preferred oilseed rape, which (along with wheat and barley) represented the largest part of the grazed area. Rape was usually grazed at during vegetation growth and flowering, while cereals were usually grazed from the milk ripe kernel stage to harvest. Damage to agricultural production was up to €20–30 per ind./year. While beaver population density in the agricultural landscape remains low, damage to agricultural production is relatively insignificant; however, field crops clearly represent an important part of the beavers’ diet in such areas, helping them survive in such open landscapes.

Abstract: In long-term individual-based field studies, several parameters need to be assessed repeatedly to fully understand the potential fitness effects on individuals. Often studies only evaluate capture stress that appears in the immediate weeks or breeding season and even long-term studies fail to evaluate the long-term effects of their capture procedures. We investigated effects of long-term repeated capture and handling of individuals in a large semi-aquatic rodent using more than 20 years of monitoring data from a beaver population in Norway. To investigate the effects, we corrected for ecological factors and analysed the importance of total capture and handling events, years of monitoring and deployment of telemetry devices on measures related to body condition, reproduction and survival of individual beavers. Body mass of dominant individuals decreased considerably with number of capture events (107 g per capture), but we found no statistically clear short or long-term effects of capture and handling on survival or other body condition indices. Annual litter size decreased with increasing number of captures among older individuals. Number of captures furthermore negatively affected reproduction in the beginning of the monitoring, but the effect decreased over the years, indicating habituation to repeated capture and handling. By assessing potential impacts on several fitness-related parameters at multiple times, we can secure the welfare of wild animal populations when planning and executing future conservation studies as well as ensure ecologically reliable research data.

Abstract 1.Wetlands are declining worldwide, and there is a great need for their restoration and creation. One natural agent of wetland engineering is beavers, Castor spp., which have returned or are returning to many parts of their former range. 2.We initially studied the facilitative effect of the beaver Castor canadensis on a waterbird community consisting of three waders and four ducks in boreal wetlands in southern Finland. Both waterbird species diversity and abundance increased when beavers impounded a pond. Common teal Anas crecca and green sandpiper Tringa ochropus were the species showing the most positive numerical response, but the other five species also increased upon flooding. 3.This article evaluates how the results of the study have been used in management, both in theory and practice. The whole-community facilitation concept has been taken up in numerous articles considering the restorative effects of beavers. It has also been used as ecological background when planning and executing man-made wetland projects in Finland within both the public and the private sectors. 4.Our study and its publication in Aquatic Conservation: Marine and Freshwater Ecosystems have set a foundation for further evidence-based management of waterbird communities. As the results show, having beavers as wetland managers is a feasible tool for creating and restoring wetlands for waterbirds and other biota. Moreover, wetland restoration projects are becoming more popular endeavours, owing to an understanding of the diverse benefits of wetlands. Flooding by beavers is used as a model for managers when creating man-made wetlands; for example, in urban areas where it is difficult to maintain beavers.

Abstract: Beaver populations are increasing throughout Europe and especially in Switzerland. Beaver are major ecological engineers of fluvial systems, dramatically influencing river morphology, ecohydrology and, consequently, aquatic and terrestrial biota. This study compared macroinvertebrate assemblages and trophic structure at two beaver complexes with contrasting topography in Switzerland over an annual cycle. One complex (Marthalen) was in a low gradient open basin, whereas the other complex (Flaach) flowed through a higher gradient ravine-like basin. Both complexes were embedded in an overall agricultural landscape matrix. Water physico-chemistry differed between the two complexes with nitrogen, phosphorus, and DOC being higher at Marthalen than at Flaach. Both complexes showed strong seasonality in physico-chemistry, but retention of nutrients (N, P) was highest in summer and only at Marthalen. Both complexes also showed strong seasonality in macroinvertebrate assemblages, although assemblages differed substantially between complexes. At Marthalen, macroinvertebrate assemblages were predominantly lentic in character at ‘pool’ sites within the complex. At Flaach, lotic macroinvertebrate assemblages were common at most sites with some lentic taxa also being present. Dietary shifts based on carbon/nitrogen stable isotopes occurred in spring and summer among sites at both complexes (autochthonous resource use increasing over allochthonous resource use downstream), although being most pronounced at Marthalen. In contrast, similar resource use across sites occurred in winter within both complexes. Although beaver significantly influenced fluvial dynamics and macroinvertebrate assemblage structure at both complexes, this influence was most pronounced at Marthalen where beaver caused the system to become more wetland in character, e.g., via higher hydraulic residence time, than at Flaach. We conclude that topography can shape beaver effects on fluvial systems and resident biota.

Abstract: Land managers are increasingly using beavers to restore hydrological function, provide wildlife habitat, and mitigate the effects of climate extremes on water balances and ecosystems. Although North American beavers (Castor canadensis) and Eurasian beavers (Castor fiber) both hold great potential for landscape-scale benefits, more information about the interactions between beavers and wildlife is necessary to maximise the ecological benefits and minimise the social and ecological costs of beaver-centred management. Beaver dams create large, deep pools with long hydroperiods, which could benefit aquatic and semi-aquatic species, especially pond-breeding amphibians, which breed in still and slow-moving water. We studied the relationship between beaver dams and pond-breeding amphibians in the southern Washington Cascade Range of the north-west U.S.A. by surveying 29 beaver-dammed and 20 undammed lentic sites in three mid-elevation (560?1,010 m) spatial blocks. We found that mean amphibian species richness was 2.7 times higher in dammed sites than in undammed sites (2.4 vs. 0.9 species). This increase in species richness was driven by increased occupancy of slow-developing species?red-legged frogs (Rana aurora) and northwestern salamanders (Ambystoma gracile), which were also more abundant at sites with dams. These two species were detected almost exclusively in beaver-dammed sites, suggesting that some amphibians rely heavily on beaver-dammed sites for successful reproduction in areas such as our study blocks where ponds and wetlands with long hydroperiods are otherwise scarce. Species with highly variable development periods?long-toed salamanders (Ambystoma macrodactylum) and rough-skinned newts (Taricha granulosa)?showed nonsignificant trends of higher site occupancy and, in the case of newts, higher number of mating events per hectare in dammed sites compared to undammed sites. Compared to undammed sites, dammed ponds were consistently deeper and had longer hydroperiods, consistent with beavers benefitting slow-developing amphibians primarily by increasing the quality of lentic breeding habitat. We suggest that slow-developing amphibians and some variable-rate developers might benefit greatly from beaver restoration, especially in areas where climate change is predicted to reduce summertime water levels. Beavers could therefore be useful and important components of ecosystem-based restoration, management, and climate adaption, especially in parts of their native ranges in North America or Eurasia predicted to undergo climatic drying.

Abstract: Dogs Canis lupus familiaris are increasingly being used in wildlife conservation studies, due to their extensive ofactory capabilities. Dogs are a useful tool for species detection, species discrimination (or subspecies), and scent-matching of individuals within a species. Scent-matching can reduce or eliminate the need for expensive genotyping of obtained biological samples. We investigated the potential use of dogs to scent-match individual Eurasian beavers Castor fiber via anal gland secretion (AGS) samples, in 30 double blind floor platform experiments. We hypothesised that dogs can scent-match individual beavers when presented with AGS from different beavers of both sexes. We showed that dogs were able to scent-match individual beavers with average accuracy of 88.9%, sensitivity of 66.7% and specificity of 93.3%. Our results suggest that scent-matching dogs may be used as a reliable additional method to DNA analysing of biological samples to improve accuracy of individual beaver detection, and a better alternative than live-trapping/capturing in monitoring of specific beavers in e.g. a reintroduction project.

Throughout the animal kingdom, antipredator mechanisms are an evolutionary driving force to enable the survival of species classified as prey. Information regarding a predator’s location can be determined through chemosensory cues from urine, faeces, visual and/or acoustic signals and anal gland secretions; and in several lab and field-based studies it has been seen that these cues mediate behavioural changes within prey species. These behaviours are often linked to fear and avoidance, which will in turn increase the prey’s survival rate. In many studies dogs (Canis lupus familiaris) have been used as a predator species, however, no research has addressed a dog’s innate ability to detect predator scents, hence the rationale behind this study. We assessed the innate ability of the untrained domestic dog to detect faecal scents of wild Eurasian brown bear (Ursus arctos arctos) and European lynx (Lynx lynx). The study monitored 82 domestic dogs across the UK and Norway. The dogs were exposed to the two predator faecal scents from Eurasian brown bear and European lynx, a herbivore faecal scent of Eurasian beaver (Castor fiber) and water control. Measurements were taken upon the time spent within a 40 cm radius of each scent and changes in the dog’s heart rate when within this 40 cm radius. We found dogs spent a decreased length of time around the predator scents and had an increased heart rate in relation to their basal heart rate. We conclude that dogs can innately sense predator scents of brown bear and lynx and elicit fear towards these odours, as shown through behavioural and physiological changes.

Abstract: The article presents research on changes in distribution of beaver families based on evaluation of beaver activity signs in the District of Snina on the area of 805 km2. The goal is to present current knowledge on the local population distribution and dynamics of Eurasian beaver summarizing and comparing data of monitoring period 2018/2019 and previous research conducted in 2014/2015. Using spatial visualisation of beaver activity signs we estimate that there are 34 (±3) beaver families present in study area. It means increase ca. 162% (±129–205%) during the period of 3–4 years. Based on current inventory results one beaver family is distributed over the territory of 23 km2. The mean length of waterway covered by each beaver family was 3.3 km (in the instance of Water Reservoir Starina we take into account the bank of reservoir), while 0.65 km (±0.49–0.85 km) is actively influenced by beavers within given stretch of stream. In the instance of Water Reservoir Starina the length patrolled by one beaver family is 2.1 km of the bank, while part of 0.79 km (±0.69–0.92 km) is actively influenced by beavers within it. The length of related part of river Cirocha (under the Water Reservoir Starina) for one beaver family is 2.3 km, while 0.95 km (±0.85–1.04 km) is actively influenced by beavers. The length of related part of small streams/tributaries is 4.4 km for one beaver family, while 0.61 km (±0.45–0.83 km) is actively influenced by beavers.

Sun, L., Muller-Schwarze, D. & Schulte, B. (2020) Dispersal pattern and effective population size of the beaver. Canadian Journal of Zoology 78(3).

Abstract: The dispersal pattern of the beaver (Castor canadensis) was studied by intensive livetrapping, tagging, and observation in Allegany State Park and its vicinity in New York from 1984 to 1996. The majority (74%) of dispersing beavers (n = 46) initiated dispersal in a downstream direction after spring ice-out. Females dispersed significantly farther away from their natal colonies than males (10.15 ± 2.42 (SE) km vs. 3.49 ± 0.86 km). Movements to neighboring sites were common (16 of 46 dispersers), indicating that beavers, especially males, may prefer to disperse to the nearest available sites. Most (64%) natal dispersers were 2-year-olds. Three-year-olds also constituted a considerable proportion (21%) of the dispersers, but 1-year-old dispersers were relatively rare (14%). Many adults underwent secondary dispersal after successful natal dispersal in our study area. Male secondary dispersers were more inclined to take over neighboring sites than were male natal dispersers (10 of 13 vs. 3 of 13). The effective population size in a 250-km2 area was estimated to be 161-228 individuals by the areal method and 267-378 individuals by the 85th percentile method.

Abstract: Reintroductions offer a powerful tool to reverse adverse anthropogenic impacts on biodiversity by restoring extirpated populations within the indigenous range of species. Reintroductions have become popular and have been increasingly used over the last decades. However, this species-centred conservation approach has been criticized for being taxonomically biased and for focusing on large and charismatic species. Studies investigating taxonomic biases in the allocation of reintroduction efforts at large scale generally consider taxonomic bias within and among higher taxa (e.g. vertebrates, plants), by comparing the number of reintroduced species within a taxon to its prevalence in nature. Here, we show that the bias is even more striking when accounting for the differences in the number of implemented programs among reintroduced species. We conducted a comprehensive search of the peer-reviewed and grey literature to inventory reintroduction programs of European terrestrial mammals. We identified 28 species that have been reintroduced at least one time. For each reintroduced mammal, we extensively searched two literature search engines and found 414 relevant publications, which described 375 distinguishable reintroduction programs implemented in Europe from the early 20th century to 2013. We used the number of implemented programs and the number of associated publications to investigate the distribution of reintroduction efforts among species. Our results show a substantial heterogeneity in the allocation of reintroduction efforts, with 68% of implemented reintroductions in Europe involving only three species: the beaver (Castor fiber), the Alpine ibex (Capra ibex) and the European bison (Bison bonasus).

Abstract: We aimed to recognise beaver-produced ecosystem services and quantify their theoretical value for the entire Northern Hemisphere. Activity of the Eurasian beaver Castor fiber and the North American beaver Castor canadensis in the landscape provides ecosystem services and disservices. Services produced by beaver activity include water purification, moderation of extreme events, habitat and biodiversity provision, nutrient cycling, greenhouse gas sequestration, recreational hunting and fishing, water supply, and non-consumptive recreation. Beaver-produced services have not been compiled, analysed, or quantified previously. Each service we evaluated is worth millions to hundreds of millions of US dollars (USD) annually. Habitat and biodiversity provision (133 million USD), along with greenhouse gas sequestration (75 million USD), are particularly valuable services in absolute terms, while non-consumptive recreation (167 USD ha?1) and habitat and biodiversity provision (133 USD ha?1) have the largest annual per-hectare values. Our results can be used to broaden decision-making and management perspectives, as we offer value estimates to wildlife managers and municipality planners for assessing local site-specific beaver wetland values and the opportunities for their realisation. Implementing Payments for Ecosystem Services schemes offer a concrete way for societies to benefit from beaver-produced services while concurrently compensating beaver-produced losses accrued to landowners. Building such schemes offer long-term realisation of ecosystem services and damage mitigation. This would lead to increased societal well-being and increased conservation interest and efforts.

Abstract: Camera trapping, paired with analytical methods for estimating species occurrence, population size or density, can yield information with direct consequences for wildlife management and conservation. Detectability, the ability to detect a species or individual if it is present, affects the reliability and efficiency of camera trap surveys and, in turn, varies across species, space and time. Greater detectability means greater sample size, and a common approach to boost detectability of wildlife by camera traps involves the application of olfactory lures. Using a camera trap study on sympatric mesocarnivores (European badger Meles meles, red fox Vulpes vulpes, pine marten Martes martes and domestic cat Felis catus), we quantified three elements of detectability: (1) the time until first detection (?sooner?, conditional on being present), (2) the proximity to a focal point in front of the camera (?closer?, conditional on being detected) and (3) the duration of exposure to the camera (?longer?, conditional on being detected). A hierarchical analytical approach and a quasi-experimental setup allowed us to test for and quantify the species-specific effect of olfactory lures on these aspects of detectability. Depending on species, average median time to first detection ranged from 4 to 28 days, distance to the focal point from 0.3 to 0.8 body lengths, and median time to departure from 2 to 6  seconds. Credible intervals overlapped substantially between most species in all three measures, and variation between observations was extensive. We detected effects of lures on time to first detection for cats (castoreum; American beaver Castor canadensis scent), distance to focal point for badgers (striped skunk Mephitis mephitis scent) and martens (castoreum, fox and skunk scents), and the duration of exposure for foxes (fox and skunk scents). We discuss how a multifaceted perspective on detectability in camera trap studies, linked with species biology, can give investigators a more structured approach to selecting and testing measures intended to boost detection probability.

The Castor fiber or Eurasian beaver can change its habitat by building dams and creating ponds. For this reason, Castor fiber is known as an “ecosystem engineer” for aquatic and riparian environments. Despite its ecological importance, at the beginning of the 20th century the population was reduced to only 1200 beavers in Europe and Asia, due to uncontrolled hunting. Recently, some reintroductions and translocations have partly re-established the population. In Italy, however, the beaver disappeared in the 16th century and no action has been taken despite the recommendation of the Council of Europe to perform a feasibility study. This research evaluates beaver reintroduction and identifies suitable areas in Italy and, in particular, in the Piedmont region. In order to achieve this, a SWOT analysis combined with a Spatial Multicriteria Analysis was performed. Firstly, the zoological and ethological aspects concerning this rodent were studied, as well as the historical reasons that led to its disappearance in Italy and near extinction in Eurasia. Secondly, Strengths, Weaknesses, Opportunities and Threats (SWOT) of the territory were identified for beaver reintroduction. The SWOT analysis was implemented, as the starting point for the spatial multicriteria analysis. Thirdly, the Multicriteria Spatial Decision Support System (MC-SDSS) was structured into two criteria, i.e. Potentials and Criticalities, representing the spatialization of strengths and weaknesses. The final result of the MC-SDSS is a map showing suitable areas for beaver reintroduction in Piedmont. This map is the weighted sum of the maps of criticalities and potentialities, performed through a set of GIS operations and weighted through a pairwise comparison of criteria by experts. The analysis was conducted for the Piedmont region, but the integrated approach and the set of criteria can also be applied in other regions. Moreover, this mixed-method approach takes into account the characteristics necessary for the choice of suitable beaver habitats and also includes economic and social aspects. Therefore, it is an improvement on the Habitat Suitability Index (HIS), generally used in reintroductions. The aspects considered in the analysis are fundamental for the future development of a shared action plan, which considers both technical and social motivations and acts for the long-term on a wide area.

Rewilding is a distinctive form of ecological restoration that has emerged quite publicly within environmental policy and conservation advocacy circles. One of the fundamental tenets of rewilding is its emphasis on non-human autonomy, yet empirical examples that examine non-human autonomy are currently limited. While there is a growing body of literature on the biopolitics of broader environmental conservation strategies, there is comparatively little scholarship on the biopolitics of rewilding. This paper argues that autonomy should not be used as a boundary marker to denote ‘wild’ non-humans, but as a situated condition that is variable across locations. It offers an empirical study of the biopolitics that govern the different expressions of non-human autonomy at two different locations in Scotland, where beavers have been reintroduced. The findings reveal how, depending on location and context, modes of governance related to rewilding strategies co-exist and interplay with animal autonomy and forms of power in contradictory ways.

Abstract: Beavers are an exception among animals in terms of the scale of environmental transformations they achieve. This study investigated primary environmental factors influencing the occurrence of aquatic invertebrates in lowland streams inhabited by the Eurasian beaver. The study was conducted in two forest streams inhabited by beavers, and in an uninhabited stream. In streams inhabited by beavers, the study covered seven ponds. Sections with flowing water were also analysed analysed downstream and upstream of the ponds. Benthos and water samples were collected at each site. Dissolved oxygen (DO) concentration and saturation were the only physicochemical parameters that indicated decreases in water quality in beaver ponds. The benthic communities of different beaver ponds were similar. The taxa that exerted the greatest influence on the similarity of the invertebrate fauna in the ponds were Oligochaeta and Chironomidae. Ostracods were also abundant in the ponds, whereas they were few in the flowing sections. Mayflies (Cloeon) and caddisflies belonging to the family Phryganeidae were also closely associated with the ponds. Caddisflies (Plectrocnemia and Sericostoma), mayflies (Baetis), and stoneflies (Nemourella and Leuctra) exhibited the highest correlation with DO concentrations, which is typical of flowing sections, and avoided stream fragments dammed by beavers. Bivalvia (Pisidium) were also abundant in each of the streams along the flowing sections. The highest number of taxa and greatest taxonomic diversity was observed in sections flowing below the beaver ponds. The engineering activity of beavers transformed the studied lowland streams, resulting in the development of rheophilic and stagnophilic communities of aquatic invertebrates, in free-flowing and dammed sections respectively.

Abstract: The Eurasian beaver (Castor fiber) is an intensely expansionary species. Species reintroductions, which were conducted in various parts of Europe, as well as the rate of natural increase have resulted in the growth of the number of individuals. The dynamic development of the beaver population in Europe means that the available data concerning the quantity of beavers becomes outdated very quickly. The purpose of this manuscript is to update the available information about the beaver populations in all countries of Europe. The information was collected in the second half of 2019. Some of the data collected include generally available studies and articles. For some countries, the author had difficulty obtaining any data; therefore, personal communication was employed with various governmental or scientific units in the given country. The outcomes of the conducted analyses were figures about the Eurasian beaver population throughout Europe. It was found that the Eurasian beaver population in Europe numbered nearly 1,222,000 individuals.

Abstract: In the medieval period, beavers were widespread throughout Poland. In the 13th century, the number of animals began to decline. After the Second World War, it was assumed that Eurasian beavers were no longer present in Poland. In 1974, the programme “Active protection of European beavers in Poland” was launched. Reintroduction was a very important element of the active protection of beavers. According to an inventory carried out in 1977, there were estimated to be over 1000 individuals. Long-term reintroduction efforts by hunters and scientists have caused beavers to be present throughout Poland. In recent years, the beaver population has increased significantly. This situation has created conflicts between farmers, foresters and beavers. In Poland, the beaver is considered a partly protected species. This manuscript discusses the dynamics of the beaver population in Poland and needed actions for future sustainable management.

2019

Abstract: Habitat requirements largely determine the distribution and abundance of a species. An invasive species can therefore threaten the survival of a native species, if the two species are similar in niche use. In Finland, the distribution of the invasive North American beaver (Castor canadensis) is approaching the range of the native Eurasian beaver (Castor fiber) possibly creating a threat for the latter. We compared the habitat use of the native and invasive beaver species in Finland in the main distribution of the species and within a smaller area where the species live in sympatry. We compared the used habitats (volume of birch and other deciduous trees and distance to agricultural and urban areas) at beaver lodges and at random locations in the available riparian habitat with (conditional) logistic regression models. Results indicated that the native beaver lodges were located closer to agriculture than those of the invasive beaver. The volume of birch was also slightly greater near the lodges of the native beaver than those of the invasive beaver. However, habitat use of both of the species seemed quite flexible, because the habitat near lodges did not differ much from the available habitat. We conclude that the probability that the North American beaver will invade the distribution area of the Eurasian beaver in Finland depends, at least partly, on the ability of the former to live in proximity to agricultural areas. However, methods other than those related to managing habitat quality may be the best approach to controlling the invasive species.

Abstract: International Union for the Conservation of Nature (IUCN) guidelines state that anticipated impacts must be considered in wildlife reintroduction, including the impacts on humans. Further, since reintroduction projects can be halted by resulting human–wildlife conflicts or human–human conflicts about wildlife, the perceptions of stakeholders and publics are of great importance. Eurasian beaver (Castor fiber) reintroduction is being debated in Great Britain at a devolved level. A decision has already been taken in Scotland to allow beavers already present to remain, while a number of reintroduction trials are taking place in England (both fenced and unfenced). There are also proposals for a reintroduction trial in Wales. We use a sub‐set of results from a nationwide survey (n = 2,759) to identify four social areas that we propose decision‐makers should consider in the debate: key stakeholder perceptions; engagement methods; attitudes towards legal protection and management responsibilities; and support for management techniques. In this paper, we investigate the complex social dimensions of wildlife reintroduction and we argue that emphasis should be placed on the need to recognise societal perceptions of potential management solutions, beyond perceptions of reintroduction itself. This is paramount in order to develop a management strategy that is more likely to garner social support and reduce potential future conflicts, should beaver reintroduction proceed. Wildlife reintroduction projects can be halted by potential human–wildlife conflicts or human–human conflicts about wildlife. Eurasian beaver (Castor fiber) reintroduction is being debated in Great Britain with decision‐making devolved to the Scottish, English, and Welsh governments. We use a subset of results from a nationwide survey (n = 2,759) to identify four social areas that we propose decision‐makers should consider and we argue that emphasis should be placed on the need to recognise societal perceptions of potential management solutions, beyond perceptions of reintroduction itself, to develop a management strategy more likely to reduce potential future conflicts.

Bush, B. M., Stenert, C., Maltchik, L. & Batzer, D. P. (2019) Beaver-created successional gradients increase β-diversity of invertebrates by turnover in stream-wetland complexes. Freshwater Biology 64(7): 1265-1274.

Abstract: Beavers are ecosystem engineers known to modify the environment primarily via dam building. Beaver wetlands are complexes of newly created, mature, and abandoned beaver constructions within a stream network. Invertebrate dynamics across all habitats derived from these successional stages remains poorly explored. Here, we test how this natural successional gradient created by beaver affects invertebrate ?-diversity and its components (turnover and nestedness). Invertebrates were sampled in the Piedmont region of Georgia (U.S.A.) in two seasons (autumn and spring) in each of four stages of habitat succession: natural stream channels, forested wetlands created by newly formed beaver dams, mature open wetland marshes, and abandoned wetland meadows. In autumn, invertebrate communities were different among successional stages, apart from new versus abandoned wetlands and new versus mature wetlands, which were only marginally different, and streams versus abandoned wetlands. In spring, only the mature beaver wetland communities were unique, differing from both streams and from newly formed or abandoned wetlands. Beta-diversity was nearly twice as high for the overall study-system than any individual successional stage, which all had similar diversity. Additionally, turnover was significantly higher than nestedness in all stages. Community differences combined with high turnover among successional stages indicates that beaver wetland communities are not merely a subset of more stable mature wetlands or streams; instead, each stage has a different taxonomic make-up. Our results strengthen the idea that beaver activity can be an important conservation tool by contributing substantially to diversity in areas where they are present. Beaver wetlands have the potential to help stabilise ?- and regional diversity in the face of wetland loss from climate change and other human impacts.

The Scottish Beaver Trial (SBT) reintroduced the Eurasian beaver (Castor fiber) in 2009 using wild-caught Norwegian beavers. This included a six-month prerelease quarantine in Devon, England. The International Union for Conservation of Nature (IUCN) and government guidelines for health screening were followed, including testing for Leptospira species. Unlicensed beavers, from Germany, were also identified in Scotland (Tayside) and Devon (later forming the River Otter Beaver Trial (ROBT)) and were health-screened under licence. Due to positive Leptospira species results and lack of prerelease screening in ROBT and Tayside, beavers from Germany and Norway (range sources) were screened. One hundred and fifty-six samples from 151 beavers were analysed by Leptospira species quantitative PCR (qPCR) (n=73 kidney (postmortem)/urine samples (antemortem)) or microscopic agglutination test (MAT, Leptospira pools 1–6) (n=83 serum samples). No beavers from Norway (95 per cent confidence interval (CI) 0–5.6 per cent, n=52), Tayside or SBT postrelease (95 per cent CI 0–4.6 per cent, n=63) tested positive. Seven beavers from Germany and Devon were positive. This gives an overall 9.3 per cent (95 per cent CI 5.2-15.1 per cent) exposure level, of which 4.6 per cent (95 per cent CI 1.9-9.3 per cent) suggested infection on a positive qPCR (n=1) or MAT titre of at least 1/400 (n=6), although none had abnormal physical, biochemical or haematological changes. This study suggests that Leptospira species infection in wild Eurasian beavers occurs at a low level, has no sex bias and does not appear to cause significant morbidity or mortality.

Abstract: Hantaviruses are RNA viruses (order Bunyavirales, family Hantaviridae) found in rodent, bat and insectivore reservoir-hosts and have been reported as an emerging significant zoonotic risk in Europe. As part of two native semiaquatic rodent restoration projects, tissue and urine samples were tested for hantavirus from water voles (Arvicola amphibius) (n=26, in 2015) and Eurasian beavers (Castor fiber) (n=20, covering 2010–2015) using a pan-hantavirus nested real-time PCR test. Kidney and lung samples were also analysed by light microscopy after haematoxylin and eosin staining of formalin-fixed paraffin wax sections. Individuals selected included those forming the source of release animals and from those already free-living in Britain in areas targeted for release, to identify existing reservoirs. For water voles all tested individuals were from Britain (n=26); for beavers some were from Britain (Scotland) (n=9) and some were samples from wild Norwegian (Telemark region) (n=6) and German (Bavaria region) animals (n=5) that formed the source of accepted wild populations currently present in Scotland. All samples tested from both species were negative for hantavirus RNA and showed no significant histopathological changes suggesting that reservoir infection with hantavirus in water voles in Britain and Eurasian beavers present in Britain, Norway and Bavaria, Germany, is unlikely.

Abstract:

  1. Eurasian beavers Castor fiber are potential hosts for a range of infectious diseases and parasites, including those typical of common European rodents. A number of infectious organisms are potentially zoonotic and may be notifiable under animal health legislation. The official trial beaver reintroductions to Scotland, the retrospectively licensed releases in England, and the increasingly obvious presence of large numbers of unlicensed illegally released animals have highlighted potential disease risks.
  2. We aimed to conduct a disease risk analysis, based on peer reviewed publications, for selection and health screening of Eurasian beavers prior to release into the wild in Britain.
  3. Adapted from the International Union for the Conservation of Nature’s ‘Guidelines for Disease Risk Analysis’, a four‐step process was used to formulate a disease risk analysis: 1) problem description; 2) hazard identification based on literature review; 3) risk assessment, which resulted in categorisation of pathogens into low, medium, and high risk; and 4) risk management: identification of mitigating measures, followed by risk re‐evaluation in light of the reported effectiveness of the mitigation measures.
  4. The highest‐risk pathogens identified in the literature review process included: parasites, specifically Cryptosporidium parvum,Echinococcus multilocularis, Eimeriaspp., Fasciola hepatica, Giardia spp., Trichinella britovi; bacteria, specifically Escherichia coli,Franciscella tularensis, Mycobacterium avium,Salmonella spp., Yersinia spp.; a fungus Cryptosporidium parvum(Emmonsia parva); and terrestrial rabies virus. Most could be mitigated by sourcing beavers from Britain. The rest could be mitigated by pre‐release testing procedures that are already established.
  5. The risk of introducing significant disease to humans, domestic animals, or wildlife by releasing into the wild in Britain a beaver that was captive‐bred in Britain or a wild beaver from Scotland, based on the current evidence of disease incidence, and assuming the use of robust, peer reviewed, pre‐release health screening techniques, can be viewed as low.

Abstract: Aim To determine whether reintroduced beavers, as an example of native herbivorous megafauna, can increase freshwater biodiversity at the landscape scale and to compare effects on two contrasting taxonomic groups. Location South-central Sweden. Methods We collected data on plant and water beetle composition and supporting environmental variables from 20 closely located wetlands, half created from the damming of streams by beavers?beaver ponds (BP), and half by other, mainly natural (e.g. topographic, river migration) means?other wetlands (OW). Differences in species composition and plant growth strategy (i.e. competitor, stress tolerator or ruderal) between wetland types were assessed using multivariate analyses. Results The species pool of both taxonomic groups was higher in BP than OW (plants + 17%; beetles + 15%). For both groups, the number of species unique to BP was 50% higher than those unique to OW. Plant and beetle compositions differed significantly between wetlands, most strongly for plants, while rarity scores showed no difference, and the incidence of invasive species was negligible. Plant composition was mostly influenced by open water, bare ground and woody debris in BP, and plant cover, height and leaf litter in OW. This was consistent with the characterization of BP vegetation by ruderal plants and OW by competitors and stress tolerators. A significant residual effect of wetland type on plant, but not beetle composition, suggests that beavers exert important direct effects on some biota (e.g. via herbivory) independent of the indirect effects they exert via environmental change. Main conclusions Beaver-created ponds support novel biodiversity that is not merely a subset of that found elsewhere in the same landscape. As such, re-establishing beaver populations where they are native should benefit freshwater biodiversity, but effects may be context and taxon specific. Beavers alone cannot solve the freshwater biodiversity crisis, but recognizing the widespread importance of herbivorous megafauna in maintaining heterogeneity and creating novel habitat will be a positive step.

Abstract 1.Territoriality is an important process shaping population dynamics, and the defense of a territory is crucial for individuals to increase the duration of territory occupancy and consequently, reproductive success. However, little is known about how the frequency of territory intrusions and subsequent territorial behaviors and aggression by territory owners are affected by external factors, such as population density. This is important, because it can affect mate change (the replacement of one pair member) and dispersal, a key ecological process. 2.The aim of this study was to investigate the behavioral and spatial response of territory owners to intruder pressure as a function of population density in a territorial, monogamous mammal, the Eurasian beaver (Castor fiber). 3.Using a combination of GPS technology, scent experiments, camera trap data, and tail scar observations from an individual-based long-term study, we investigated the factors influencing spatial movement patterns by territory owners in response to a simulated intruder, and the factors affecting territory intrusions. 4.We found consistent inverse density-dependent patterns in territorial behaviors and evidence of conspecific aggression. At lower densities, territory owners detected more simulated intrusions, showed more territorial reactions, and experienced increased conspecific aggression as indicated by tail scars, suggesting increased intruder pressure. 5.Inverse density-dependent territorial behavior and aggression suggest a potential mechanistic link between inverse density-dependent natal dispersal and mate change. At low population densities, increased dispersal amplifies intruder pressure, leading to the observed increases in territorial behaviors, conspecific aggression, and previously observed mate turnover, which in turn might increase natal dispersal. Our study demonstrates how population density can affect the behavior and space use of individuals, which is important for territory occupancy and fitness.

Abstract: Beavers are ecosystem engineers which are capable to facilitate many groups of organisms. However, their facilitation of mammals has been little studied. We applied two methods, camera trapping and snow track survey to investigate the facilitation of a mammalian community by the ecosystem engineering of the American beaver (Castor canadensis) in a boreal setting. We found that both mammalian species richness (83% increase) and occurrence (12% increase) were significantly higher in beaver patches than in the controls. Of individual species, the moose (Alces alces) used beaver patches more during both the ice-free season and winter. The Eurasian otter (Lutra lutra), the pine marten (Martes martes) and the least weasel (Mustela nivalis) made more use of beaver sites during the winter. Our study highlights the role of ecosystem engineers in promoting species richness and abundance, especially in areas of relatively low productivity. Wetlands and their species have been in drastic decline during the past century, and promoting facilitative ecosystem engineering by beaver is feasible in habitat conservation or restoration. Beaver engineering may be especially valuable in landscapes artificially deficient in wetlands.

Our goal is to assess consequences of the introduction of alien North American (Castor canadensis (Cc)) beaver into the Nature Reserves inhabited by Eurasian beaver (Castor fiber (Cf)) in European Russia using a mathematical model. For this reason, we have developed a two-species model of population dynamics. Long-term (1934–2015) monitoring data on Cf population dynamics in six Nature Reserves are used in computer modelling of competitive interactions between native Cf and alien Cö. The Reserves are located in the European part of Russia in the north, south, and central part of Cf range. We have simulated the dynamics of both species populations after the introduction of Cö into the habitats occupied by Cf. The model demonstrates that Cf is displaced by Cc in all the Reserves after the introduction of 2 – 24 individuals of Cö. However, the duration of exclusion of one species by the other varies as a function of ecological conditions, initial number of individuals, and fecundities. Our model shows that, in case of introduction of 12 Cö beavers, the size of Cf population starts to decrease after 31–146 years as a result of competition. We study the conditions providing the coexistence of both species and find that Cö population dynamics after Cf exclusion can be described by four patterns: irruptive (Lapland Reserve), single-stage (Prioksko-Terrasny Reserve), multi-stage (Darwin, Central-Forest, and Khoper Reserves) and logistic population growth (Oka Reserve). Species biology in terms of the fecundity, family size, rate of individual development until sexual maturity, life-span, and the age structure of populations are compared between species to detect the mechanisms providing the competitive advantage of Cö over Cf.

Abstract: Recognition that beavers are integral components of stream ecosystems has resulted in an increase in beaver-mediated habitat restoration projects. Beaver restoration projects are frequently implemented in degraded stream systems with little or no beaver activity. However, selection of restoration sites is often based on habitat suitability research comparing well-established beaver colonies to unoccupied stream sections or abandoned colonies. Because beavers dramatically alter areas they occupy, assessing habitat conditions at active colonies may over-emphasize habitat characteristics that are modified by beaver activity. During 2015?2017, we conducted beaver activity surveys on streams in the upper Missouri River watershed in southwest Montana, U.S.A, to investigate habitat selection by beavers starting new colonies in novel areas. We compared new colony locations in unmodified stream segments to unsettled segments to evaluate conditions that promoted colonization. Newly settled stream segments had relatively low gradients (??±?SE = ?0.72?±?0.27), narrow channels (? = ?1.31?±?0.46 high channel complexity (? = 0.76?±?0.42), high canopy cover of woody riparian vegetation (? = 0.56?±?0.21), and low-lying areas directly adjacent to the stream (? = 0.36?±?0.24), where ? denotes covariate effect sizes. Habitat selection patterns differed between our new settlement site analysis and an analysis of occupied versus unoccupied stream segments, suggesting that assessing habitat suitability based on active colonies may result in misidentification of suitable site conditions for beaver restoration. Our research provides recommendations for beaver restoration practitioners to select restoration sites that will have the highest probability of successful colony establishment.

Rosell, F., Cross, H. B., Johnsen, C. B., Sundell, J. & Zedrosser, A. (2019) Scent-sniffing dogs can discriminate between native Eurasian and invasive North American beavers. Scientific Reports 9(1): 15952.

The invasion of a species can cause population reduction or extinction of a similar native species due to replacement competition. There is a potential risk that the native Eurasian beaver (Castor fiber) may eventually be competitively excluded by the invasive North American beaver (C. canadensis) from areas where they overlap in Eurasia. Yet currently available methods of census and population estimates are costly and time-consuming. In a laboratory environment, we investigated the potential of using dogs (Canis lupus familiaris) as a conservation tool to determine whether the Eurasian or the North American beaver is present in a specific beaver colony. We hypothesized that dogs can discriminate between the two beaver species, via the odorant signal of castoreum from males and females, in two floor platform experiments. We show that dogs detect scent differences between the two species, both from dead beaver samples and from scent marks collected in the field. Our results suggest that dogs can be used as an “animal biosensor” to discriminate olfactory signals of beaver species, however more tests are needed. Next step should be to test if dogs discern between beaver species in the field under a range of weather conditions and habitat types and use beaver samples collected from areas where the two species share the same habitat. So far, our results show that dogs can be used as a promising tool in the future to promote conservation of the native beaver species and eradication of the invasive one. We therefore conclude that dogs may be an efficient non-invasive tool to help conservationist to manage invasive species in Europe, and advocate for European wildlife agencies to invest in this new tool.

Abstract: Dams are recognised to impact aquatic biodiversity, but the effects and conclusions diverge across studies and locations. By using a meta-analytical approach, we quantified the effects of impoundment on fish communities distributed across three large biomes. The impacts of dams on richness and diversity differed across biomes, with significant declines in the tropics, lower amplitude but similar directional changes in temperate regions, and no changes in boreal regions. Our analyses showed that non-native species increased significantly in tropical and temperate regulated rivers, but not in boreal rivers. In contrast, temporal trajectories in fish assemblage metrics were common across regions, with all biomes showing an increase in mean trophic level position and in the proportion of generalist species after impoundment. Such changes in fish assemblages may affect food web stability and merit closer study. Across the literature examined, predominant mechanisms that render fish assemblages susceptible to impacts from dams were: (1) the transformation of the lotic environment into a lentic environment; (2) habitat fragmentation and (3) the introduction of non-native species. Collectively, our results highlight that an understanding of the regional context and a suite of community metrics are needed to make robust predictions about how fish will respond to river impoundments.

Abstract: Understanding changes in macroinvertebrate communities is important because they play a large role in stream ecosystem functioning, and they are an important food resource for fish. Beaver-induced changes to stream morphology could alter macroinvertebrate communities, which in turn could affect food webs and ecosystem function. However, studies investigating the effects of North American beaver activities on macroinvertebrates are rare in the inter-mountain west, an area with high potential for beaver-assisted restoration. The aim of this study was to quantify differences in the macroinvertebrate community between unaltered segments of streams and within beaver ponds in north-eastern Utah, U.S.A. We assessed macroinvertebrate species richness, biomass, density, functional feeding group composition, mobility group composition, and macroinvertebrate habitat characteristics to test the hypothesis that macroinvertebrate communities will differ among habitat types (undammed stream segments and beaver ponds) in beaver-occupied streams. Beaver pond communities significantly differed from lotic reach communities in many ways. Beaver ponds were less diverse with 25% fewer species. Although there was variability among streams, in general, beaver ponds had 75% fewer individuals and 90% lower total macroinvertebrate biomass compared to lotic reaches. Regarding functional feeding groups, beaver ponds contained more engulfers, while lotic reaches contained more scrapers, filterers, and gatherers. For mobility groups, beaver ponds had more sprawlers, while lotic reaches had more clingers. Swimmers were also more prevalent in lotic reaches, although this is probably due to the abundance of Baetis within lotic reaches. More beaver pond taxa were classified as lentic-dwelling insects, while more lotic reach taxa were categorised as preferring lotic habitats. The creation of ponds by beavers fundamentally altered the macroinvertebrate community in north-eastern Utah streams. Such changes to stream macroinvertebrate communities suggest that recolonisation of beavers across North America may be altering stream functioning and food webs. Our study highlights the need to further investigate the effects of beaver recolonisation on stream communities.

Abstract: The Eurasian beaver (Castor fiber) is an intensely expansionary species. Species reintroductions, which were conducted in various parts of Europe, as well as the rate of natural increase have resulted in the growth of the number of individuals. The dynamic development of the beaver population in Europe means that the available data concerning the quantity of beavers becomes outdated very quickly. The purpose of this manuscript is to update the available information about the beaver populations in all countries of Europe. The information was collected in the second half of 2019. Some of the data collected include generally available studies and articles. For some countries, the author had difficulty obtaining any data; therefore, personal communication was employed with various governmental or scientific units in the given country. The outcomes of the conducted analyses were figures about the Eurasian beaver population throughout Europe. It was found that the Eurasian beaver population in Europe numbered nearly 1,222,000 individuals.

Abstract: We evaluated habitat selection by European beaver Castor fiber L. across a spatial gradient from local (within the family territory) to a broad, ecoregional scale. Based on aerial photography, we assessed the habitat composition of 150 beaver territories along the main water bodies of the Vistula River delta (northern Poland) and compared these data with 183 randomly selected sites not occupied by the species. The beavers preferred habitats with high availability of woody plants, including shrubs, and avoided anthropogenically modified habitats, such as arable lands. Within a single family territory, we observed decreasing woody plant cover with increasing distance from a colony centre, which suggests that beaver habitat preferences depend on the assessment of both the abundance and spatial distribution of preferred habitat elements. We tested the importance of spatial scale in beaver habitat selection with principal coordinates of neighbour matrices analysis, which showed that the geographical scale explained 46.7% of the variation in habitat composition, while the local beaver density explained only 10.3% of this variability. We found two main spatial gradients that were related to the broad spatial scale: first, the most important gradient was related to the largest distances between beaver sites and was independent of woody plant cover and the local beaver site density. The second most important gradient appeared more locally and was associated with these variables. Our results indicate that European beaver habitat selection was affected by different scale-related phenomena related 1) to central place foraging behaviour, which resulted in the clumped distribution of woody plants within the territory, and 2) local population density and woody plant cover. Finally, 3) habitat selection occurs independently across the largest spatial scale studied (e.g. between watersheds), which was probably due to the limited natal dispersal range of the animals.

2018

Introduction: Human-induced global change is increasingly affecting life on our planet, including living conditions for humans themselves as well as the resources we depend on. As a result, species diversity is strongly declining.  The Living Planet Index shows a 58% global decline in populations of amphibians, fish, reptiles, mammals and birds between 1970 and 2012, varying from 36 to 38% in terrestrial and marine ecosystems to 81% in freshwater habitat. Habitat loss or degradation and overexploitation are the main causes of these steep declines. Since the worldwide expansion of modern humans (Homo sapiens) began, humans have overexploited vertebrates, with a bias to the largest animals being extirpated first, from the Late Pleistocene extinctions of terrestrial megafauna to the ongoing declines of terrestrial, marine and freshwater large-bodied animals. There is increasing evidence that this global wildlife loss, or defaunation, does not only imply the loss of charismatic animals but also the functions they have in ecosystems. To restore these missing functions, a novel ecological restoration technique has emerged, referred to as rewilding. Rewilding aims to restore natural processes in ecosystems in general, and often focuses on re-introduction of missing large wildlife species or, in case these went extinct, their proxies. Rewilding is increasingly implemented in practice globally, with a strong emphasis on Europe and the re-introduction of large herbivores.

Several studies have reported significant emission of greenhouse gasses (GHG) from beaver dams, suggesting that ponds created by beavers are a net source of CO2 and CH4. However, most evidence come from studies conducted in North America (on Castor canadensis) without a parallel comparison with the Eurasian beaver’s (Castor fiber) impacts and a critical consideration of the importance of the carbon deposition in dam sediments. The most abundant population of the Eurasian beaver lives in Russia, notably within the River Ob watershed in Western Siberia which is the second largest floodplain on Earth. Consequently, we assessed the holistic impact of Eurasian beavers on the multiple carbon pools in water and on other related biogeochemical parameters of the Ob’s floodplain streams. We compared dammed and flowing streams in a floodplain of the middle course of the river. We found that beavers in western Siberia increase the stream emission of methane by about 15 times by building their dams. This is similar to what has been documented in North America. A new finding from the present study is that Siberian beavers facilitate 1) nutrient recycling by speeding up the nutrient release from particulate organic matter; and 2) carbon sequestration by increasing the amount of dissolved organic carbon. This carbon becomes in part recalcitrant when buried in sediments and is, therefore, removed from the short-term carbon cycle. These new results should be taken into consideration in river management and provide a further reason for the conservation and management of Eurasian Beavers.

Abstract: Freshwater fishes are threatened globally, and often too little is known about threatened species to effectively guide their conservation. Habitat complexity is linked to fish species diversity and persistence, and degraded streams often lack habitat complexity. Beaver Castor spp., in turn, have been used to restore streams and increase habitat complexity. The northern leatherside chub Lepidomeda copei is a rare, small-bodied, drift-feeding minnow that has anecdotally been observed to use complex habitats associated with beaver dams in the western United States. To investigate this anecdote, we conducted fish and habitat surveys, the latter focusing on quantifying habitat complexity, in a sub-basin of the Upper Snake River Basin in the USA. Complementary generalised linear model and path analyses revealed that northern leatherside chub occurred more often at sites with complex streamflows, and streamflows were more complex when beaver dams were present and pools were deeper. Northern leatherside chubs were also more likely to occur when temperatures were warmer, aquatic macrophytes were abundant and stream channels were narrow and deep. The linkage between chubs, complex streamflows and beaver dams needs to be evaluated more broadly to completely understand its role in the rangewide status of the species. However, it does suggests that increased use of beaver reintroductions and dam analogues for stream restoration could be a boon for the northern leatherside chub, but such efforts should be monitored to determine their effectiveness to help adapt beaver-based restoration approaches to best benefit the species.

Through their dam-building activities and subsequent water storage, beaver have the potential to restore riparian ecosystems and offset some of the predicted effects of climate change by modulating streamflow. Thus, it is not surprising that reintroducing beaver to watersheds from which they have been extirpated is an often-used restoration and climate-adaptation strategy. Identifying sites for reintroduction, however, requires detailed information about habitat factors—information that is not often available at broad spatial scales. Here we explore the potential for beaver relocation throughout the Snohomish River Basin in Washington, USA with a model that identifies some of the basic building blocks of beaver habitat suitability and does so by relying solely on remotely sensed data. More specifically, we developed a generalized intrinsic potential model that draws on remotely sensed measures of stream gradient, stream width, and valley width to identify where beaver could become established if suitable vegetation were to be present. Thus, the model serves as a preliminary screening tool that can be applied over relatively large extents. We applied the model to 5,019 stream km and assessed the ability of the model to correctly predict beaver habitat by surveying for beavers in 352 stream reaches. To further assess the potential for relocation, we assessed land ownership, use, and land cover in the landscape surrounding stream reaches with varying levels of intrinsic potential. Model results showed that 33% of streams had moderate or high intrinsic potential for beaver habitat. We found that no site that was classified as having low intrinsic potential had any sign of beavers and that beaver were absent from nearly three quarters of potentially suitable sites, indicating that there are factors preventing the local population from occupying these areas. Of the riparian areas around streams with high intrinsic potential for beaver, 38% are on public lands and 17% are on large tracts of privately-owned timber land. Thus, although there are a large number of areas that could be suitable for relocation and restoration using beavers, current land use patterns may substantially limit feasibility in these areas.

Abstract Small dam removals are increasing on a global scale; yet, general predictions of organism response to dam removal are constrained by heterogeneity of study designs, implementation strategies, geographies, and characteristics of dams and their removals. Macroinvertebrate data extracted from 29 studies including 34 small dam removals over a broad geographical range were re‐analysed utilizing dam removal effect sizes (a quantified change from before to after removal). Effect sizes of 10 metrics of community structure were calculated to investigate the spatiotemporal extent of small dam removal effects and if responses differ with characteristics of the dam and environmental settings. We found that dam removal had initial negative effects on total macroinvertebrate density and Ephemeroptera, Plecoptera and Trichoptera (EPT) density, both downstream and upstream; however, recovery to pre‐removal values was reached and exceeded after c. 15–20 months. Mean annual discharge, land use in the catchment and distance from the dam affected the magnitude and direction of responses of four community metrics: total density, EPT density, %EPT density and family biotic index. Synthesis and applications. Our study provides evidence that macroinvertebrate community recovery from dam removal is mediated by catchment characteristics and system size, which may correlate with sediment flushing efficiency. Negative impacts were observed in smaller systems or those with a high percentage of undisturbed catchment areas, conditions that may benefit from sediment management prior to dam removal. Significant responses in reaches upstream of the impoundment clearly indicate that caution be applied to interpretations of response in sampling designs that utilize upstream sites for reference condition.

Abstract: Wolves (Canis lupus) can be primary predators of beavers (Castor canadensis), but little is known about wolf-beaver dynamics. We identified kills from 1 wolf (V009) of the Ash River Pack in Voyageurs National Park from 1 April to 5 November 2015 to provide direct estimates of wolf pack kill and predation rates of beavers. We documented 12 beaver kills by V009 during the 2015 ice-free season and estimated V009 killed 22 beavers during this period. Based on the number of beavers killed by V009, we estimated the Ash River Pack removed 80–88 beavers (kill rate of 0.085–0.095 beavers/wolf/day), which was 38–42% of the beaver population in their home range during the ice-free season. Even with this substantial level of predation in 2015, the beaver population in the Ash River Pack home range increased by an estimated 43% in 2016, which suggested dispersal from more densely populated adjacent areas likely compensated for the effects of wolf predation. We have presented the first direct estimate of wolf kill and predation rates on beavers, but more research is necessary to understand how wolf predation affects beaver populations under a variety of conditions. Published 2017. This article is a U.S. Government work and is in the public domain in the USA.

Abstract

* Predator–prey relationships can have wide-ranging ecological and landscape-level effects. Knowledge of these relationships is therefore crucial to understanding how these systems function and how changes in predator–prey communities affect these systems. Grey wolves Canis lupus can be significant predators of beavers Castor spp., and conversely, beavers can be important prey for wolves, but wolf-beaver dynamics in North America, Europe, and Asia are poorly understood.

* Our objectives were to synthesise current knowledge regarding wolf-beaver interactions and to identify knowledge gaps that should be targeted for study to increase our understanding of wolf-beaver dynamics.

* During the ice-free season, beavers are vulnerable to predation and can be the primary or secondary prey of wolves, but the factors that affect beaver consumption by wolves are complex and are likely dependent on biological and environmental factors.

* High beaver abundance can increase wolf pup survival, and beavers may subsidise wolves during periods of reduced ungulate abundance. Thus, many researchers have suggested that beaver densities adversely affect ungulate populations through apparent competition, though this remains largely untested.

* The effects of wolf predation on beaver population dynamics are poorly understood, as most assessments are lacking in quantitative rigor and are instead based on indirect methods (e.g. scat analysis), anecdotal evidence, or speculation. To understand the effect of predation on beaver populations fully, better estimates (e.g. from documented predation events) of wolf predation on beavers are necessary.

* Given the complexities of wolf-ungulate-beaver systems, fully understanding wolf-beaver dynamics will be challenging and is likely to require long-term, intensive research of wolf, ungulate, and beaver population parameters. Understanding this dynamic has implications, not only for the conservation and management of wolves and beavers, but also for ungulate populations, which are affected by the numerical and functional responses of wolves in these same systems.

Abstract:

* In November 2016, the Scottish Government announced that they were minded to allow the two ‘trial’ reintroduced populations of Eurasian beaver Castor fiber to remain in Scotland and be allowed to expand naturally, and that the species will receive legal protection. This was a historic moment: the first formally approved reintroduction of a mammal species anywhere in the United Kingdom.

* The issues surrounding beaver reintroduction to Scotland had been the subject of intense investigation and public debate over the previous 21 years. Extensive multidisciplinary and interdisciplinary work was performed to assess the desirability and feasibility of reintroducing the Eurasian beaver and informed the government’s decision. This was one of the most detailed assessments carried out for any species reintroduction proposal.

* The work was broadly divided into desk-based and stand-alone studies based primarily on the European and North American experience of living with beavers, the scientifically monitored Scottish Beaver Trial reintroduction in west Scotland, a study of beavers resulting from unauthorised releases in an east Scotland catchment and the work of a specialist group that examined beaver–salmonid interactions and issues.

* It was confirmed that beavers have a very positive influence on biodiversity overall, although some specific species and habitats of high conservation importance can be adversely affected if appropriate management is not in place. Beavers provide a range of ecosystem services with the potential for socio-economic benefits. However, beavers’ activities may affect some land uses, the extent and significance depending on local conditions. Management techniques are well developed, although some will require refinement and appropriate licensing within a Scottish regulatory regime. A strategic approach to developing management throughout Scotland will need to be progressed in partnership with key stakeholders.

Erich, C. P., Serena, D. & Leonard, S. (2018) Responses of macroinvertebrate communities to small dam removals: Implications for bioassessment and restoration. Journal of Applied Ecology 55(4): 1896-1907.

Abstract Small dam removals are increasing on a global scale; yet, general predictions of organism response to dam removal are constrained by heterogeneity of study designs, implementation strategies, geographies, and characteristics of dams and their removals. Macroinvertebrate data extracted from 29 studies including 34 small dam removals over a broad geographical range were re‐analysed utilizing dam removal effect sizes (a quantified change from before to after removal). Effect sizes of 10 metrics of community structure were calculated to investigate the spatiotemporal extent of small dam removal effects and if responses differ with characteristics of the dam and environmental settings. We found that dam removal had initial negative effects on total macroinvertebrate density and Ephemeroptera, Plecoptera and Trichoptera (EPT) density, both downstream and upstream; however, recovery to pre‐removal values was reached and exceeded after c. 15–20 months. Mean annual discharge, land use in the catchment and distance from the dam affected the magnitude and direction of responses of four community metrics: total density, EPT density, %EPT density and family biotic index. Synthesis and applications. Our study provides evidence that macroinvertebrate community recovery from dam removal is mediated by catchment characteristics and system size, which may correlate with sediment flushing efficiency. Negative impacts were observed in smaller systems or those with a high percentage of undisturbed catchment areas, conditions that may benefit from sediment management prior to dam removal. Significant responses in reaches upstream of the impoundment clearly indicate that caution be applied to interpretations of response in sampling designs that utilize upstream sites for reference condition.

Abstract A history of land clearance and riparian tree and wood management has resulted in limited riparian woodland and wood along British rivers. However, river management approaches are now being promoted that ?work with natural processes? to reduce flood risk through measures intended to restore, protect and emulate the natural function of catchments, rivers, estuaries and coasts. Wood has started to be reintroduced into river channels during river restoration and natural flood management activities, but this needs to be undertaken using appropriate quantities, locations and designs that mimic natural tree-wood features. This paper reviews the knowledge that is needed to support wood reintroduction activities including (i) the characteristics of the riparian tree species and wood that are present; (ii) the importance of river size relative to that of trees and wood pieces; and (iii) the way trees, wood and geomorphic processes interact across rivers and floodplains of different energy and style.

Abstract: Western U.S. rivers are currently influenced by legacy effects of reduced large wood (LW) loading and retention that has substantially reduced in-stream habitat complexity. Large wood is typically associated with streams in undisturbed old-growth forest and in the correct geomorphic context can drastically alter stream and valley habitat complexity. Streams with LW are typically multichannel and depositional, while streams lacking LW, due to relatively recent wildfire or logging (<200 years ago), are usually single channelled and erosional. We compared population biomass and individual growth rates of Brook Trout Salvelinus fontinalis in streams across a gradient of wood volumes. At both the square metre and valley length scales, standing stock biomass of aquatic invertebrates was the best predictor of trout biomass. However, at the valley scale, the number of pools was important in predicting trout biomass in combination with standing stock biomass of aquatic invertebrates. Individual growth rates of age-1 Brook Trout were negatively affected by increasing density; however, growth rates for the largest and smallest individuals at each site were unaffected by density. Our results suggest the pool habitat created by LW acts synergistically with prey availability to dramatically increase trout populations. However, in streams lacking LW, negative effects of detrimental land use practices have persisted >100 years, suggesting that recovering lost animal production in mountain stream networks will only occur at decadal to century time scales.

Abstract: Chemical communication by scent-marking is widespread among mammals and can serve different purposes, such as territory demarcation, mate attraction and self-advertisement. In this study, we examined scent-marking behavior by subordinate Eurasian beavers (Castor fiber) in a population in southeast Norway. We conducted scent experiments in 18 family groups, simulating a territory intruder using experimental scent mounds (ESM). In total, we recorded 196 territorial reactions (destroying and/or overmarking of scent mounds). Subordinates contributed 14% of all territorial reactions and first overmarked 12% of the ESM, and the number of subordinates in the family group did not increase the total number of territorial reactions. This suggests that the contribution by subordinates plays a minor role in territorial defense. The number of territorial reactions by subordinates was positively related to the age of their parents, suggesting that subordinates might take over territorial duties with increasing parental senescence, likely because they have increased chances of inheriting the territory. Increased experience in territorial activities possibly helps subordinates to successfully gain and defend a territory of their own.

We installed 12 pond levelers to counter flooding by beavers and developed a cost?benefit analysis for these sites in Alberta, Canada. We also documented beaver management approaches throughout Alberta. Over 3 years, one site required regular maintenance until we designed a modified pond leveler; another required minor modifications. Others required almost no maintenance. Based on a “willingness-to-pay” (WTP) of $0 and discount rate of 3%, installing pond levelers resulted in a present value net benefit of $81,519 over 3 years and $179,440 over 7 years. Scenarios incorporating discount rates of 3% and 7%, horizons of either 3 or 7 years, and varying WTPs resulted in significant net benefits. Provincially, municipalities employed up to seven methods to control beavers: most commonly lethal control and dam removal. Total annual costs provided by 48 municipalities and 4 provincial parks districts were $3,139,223; however, cost-accounting was sometimes incomplete, which makes this a conservative estimate.

Jepson, P., Schepers, F. & Helmer, W. (2018) Governing with nature: a European perspective on putting rewilding principles into practice. Philosophical Transactions of the Royal Society B: Biological Sciences 373(1761).

Abstract: Academic interest in rewilding is moving from commentary to discussion on future research agendas. The quality of rewilding research design will be enhanced if it is informed by knowledge of the rewilding practice. Here, we describe the conceptual origins and six case study examples of a mode of rewilding that emerged in the Dutch Delta and is being promoted and supported by Rewilding Europe, an umbrella organization established in 2011. The case experiences presented help position this version of rewilding in relation to the US 3C's version and point towards a rewilding action philosophy characterized by pragmatic realism and pioneer projects around which multiactor networks interested in policy innovation and change form. We argue that scaling-up the models of rewilding presented is constrained by institutional cultures and will require innovations in conservation finance and business models. Nonetheless, we suggest that the expanding European Rewilding Network and associated facilities, such as the European Wildlife Bank, represent a valuable asset for natural science research, aimed at exploring the ecological impacts of grazing and the relationship between role of restored herbivore guilds and biotical expansion, and for social science research investigating concepts such as non-human agency and autonomy. Lastly, we ask applied scientists to view rewilding as an uncertain and unfolding conservation approach and to refrain from seeking to specify it as a management approach supporting the delivery of pre-determined targets and/or ideals. This is because such actions may constrain the transformative potential of rewilding practice.This article is part of the theme issue ‘Trophic rewilding: consequences for ecosystems under global change’.

Abstract: 1.Territoriality is an important process shaping population dynamics, and the defense of a territory is crucial for individuals to increase the duration of territory occupancy and consequently, reproductive success. However, little is known about how the frequency of territory intrusions and subsequent territorial behaviors and aggression by territory owners are affected by external factors, such as population density. This is important, because it can affect mate change (the replacement of one pair member) and dispersal, a key ecological process. 2.The aim of this study was to investigate the behavioral and spatial response of territory owners to intruder pressure as a function of population density in a territorial, monogamous mammal, the Eurasian beaver (Castor fiber). 3.Using a combination of GPS technology, scent experiments, camera trap data, and tail scar observations from an individual-based long-term study, we investigated the factors influencing spatial movement patterns by territory owners in response to a simulated intruder, and the factors affecting territory intrusions. 4.We found consistent inverse density-dependent patterns in territorial behaviors and evidence of conspecific aggression. At lower densities, territory owners detected more simulated intrusions, showed more territorial reactions, and experienced increased conspecific aggression as indicated by tail scars, suggesting increased intruder pressure. 5.Inverse density-dependent territorial behavior and aggression suggest a potential mechanistic link between inverse density-dependent natal dispersal and mate change. At low population densities, increased dispersal amplifies intruder pressure, leading to the observed increases in territorial behaviors, conspecific aggression, and previously observed mate turnover, which in turn might increase natal dispersal. Our study demonstrates how population density can affect the behavior and space use of individuals, which is important for territory occupancy and fitness.

Environmental rearrangements by ecosystem engineers influence food-web characteristics by altering resource accessibility/availability in the newly created habitat. However, the paucity of empirical studies on this indirect interaction has hindered the integration of ecosystem engineering and food-web theory. Here, we investigated the effect of the Canadian beaver Castor canadensis on the activity, realized fecundity and ecosystem functions provided by saproxylic beetles by quantifying beetle emergence holes on woody debris within the Kouchibouguac National Park, New Brunswick, Canada. We tested the hypothesis that perturbation induced by beaver activity enhances the activity and realized fecundity of saproxylic beetles by modifying their habitat and resource accessibility. We used 16 sites identified as beaver modified, each paired with a control site <500 m away. At each site, we quantified insect emergence holes on snags at increasing distances from the watercourse. Our results suggest that engineered habitat patches enhance the activity and reproduction of saproxylic beetle species, small emergence holes from Scolytinae being only observed in abundance on small trees located close to the watercourse and large emergence holes from Cerambycidae being one third more abundant throughout beaver-modified sites. The complementary relationship between the Canadian beaver and saproxylic beetles demonstrates the potential for conservation measures encapsulating all of these organisms.

Abstract: Species distributions are shaped by numerous factors that vary in importance across spatiotemporal scale. Understanding drivers of the distribution of North American beaver (Castor canadensis Kuhl, 1820) is paramount given their profound influence on ecological communities. Our objectives were to evaluate the influence of habitat quality, risk of gray wolf (Canis lupus Linnaeus, 1758) predation, and anthropogenic disturbance on the occurrence of beaver colonies in northeast British Columbia (BC), Canada. We used mixed-effects multinomial logistic regression to model the occurrence of active and inactive colonies, and t-tests to compare landscape covariates associated with active versus inactive colonies. We determined that occurrence of beavers was driven by habitat quality. Occurrence increased in areas with higher vegetation-class richness and greater proportions of open water, nutrient-rich fen, and deciduous swamp. We also observed that active colonies were surrounded by greater amounts of deciduous swamps relative to inactive colonies. We found no evidence that predation risk or industrial activities decreased the occurrence of beavers in northeast BC; although, numerical changes in abundance might occur without changes in distribution. This research illuminated drivers of beaver distribution, while providing a means to predict the occurrence of a keystone species in the boreal ecosystem.

Abstract: Beavers are ecosystem engineers which are capable to facilitate many groups of organisms. However, their facilitation of mammals has been little studied. We applied two methods, camera trapping and snow track survey to investigate the facilitation of a mammalian community by the ecosystem engineering of the American beaver (Castor canadensis) in a boreal setting. We found that both mammalian species richness (83% increase) and occurrence (12% increase) were significantly higher in beaver patches than in the controls. Of individual species, the moose (Alces alces) used beaver patches more during both the ice-free season and winter. The Eurasian otter (Lutra lutra), the pine marten (Martes martes) and the least weasel (Mustela nivalis) made more use of beaver sites during the winter. Our study highlights the role of ecosystem engineers in promoting species richness and abundance, especially in areas of relatively low productivity. Wetlands and their species have been in drastic decline during the past century, and promoting facilitative ecosystem engineering by beaver is feasible in habitat conservation or restoration. Beaver engineering may be especially valuable in landscapes artificially deficient in wetlands.

Avian species respond to ecological variability at a range of spatial scales and according to life history stage. Beaver dams create wetland systems for waterbirds that are utilized throughout different stages of the breeding season. We studied how beaver-induced variability affected mobile pairs and more sedentary broods along with the production of Common Teal Anas crecca at the patch and landscape scale on their breeding grounds. Beavers Castor spp. are ecosystem engineers that enhance waterfowl habitats by impeding water flow and creating temporary flooding. Two landscapes in southern Finland with (Evo) and without (Nuuksio) American Beavers Castor canadensis were used in this study. To investigate the patch-scale effect, pair and brood densities along with brood production were first compared at beaver-occupied lakes and non-beaver lakes in the beaver landscape. Annual pair and brood densities/km shoreline and brood production were compared between beaver and non-beaver landscapes. Facilitative effects of beaver activity were manifest on brood density at both patch and landscape scales: these were over 90% and 60% higher in beaver patches and landscapes, respectively. An effect of beaver presence on pair density was only seen at the landscape level. Pair density did not strongly affect brood production, as shown earlier for relatively mildly density-dependent Teal populations. Because the extent of beaver flooding was a crucial factor affecting annual Teal production in the study area, we infer beaver activity has consequences for the local Teal population. Ecosystem engineering by the beaver could therefore be considered a restoration tool in areas where waterfowl are in need of high-quality habitats.

Abstract With the recent population increase in beavers (Castor spp.), a considerable amount of new riparian habitat has been created in the Holarctic. We evaluated how beaver-induced floods affect carbon (C) dynamics in the beaver ponds and in the water-atmosphere and riparian zone interfaces. Beaver disturbance affects soil organic C storage by decreasing or increasing it, resulting in a redistribution of C. Upon flooding, the concentration of dissolved organic carbon (DOC) increases in the water. This C can be released into the atmosphere, it can settle down to the bottom sediments, it can be sequestered by vegetation, or it can be transported downstream. The carbon dioxide (CO2) emissions vary between 0.14 and 11.2 g CO2 m−2 day−1, averaging 4.9 CO2 g m−2 day−1. The methane (CH4) emissions vary too, from 27 mg m−2 day−1 to 919 mg m−2 day−1, averaging 222 mg CH4 m−2 day−1. Globally, C emission from beaver ponds in the form of CH4 and CO2 may be 3.33–4.62 Tg (teragram, 1012 g) year−1. The yearly short-term sedimentation rates in beaver ponds vary between 0.4 and 47 cm year−1, and individual ponds contain 9–6355 m3 of sediment. The approximate global estimate for yearly C sedimentation is 3.8 Tg C; beaver ponds globally contain 380 Tg sedimented C. After being formed, beaver pond deposits can remain for millennia. Both C sequestration and CO2 and CH4 emissions in ponds of various ages should be taken into account when considering the net effect of beavers on the C dynamics. With present estimates, beaver ponds globally range from a sink (−0.47 Tg year−1) to a source (0.82 Tg year−1) of C. More research is needed with continuous flux measurements and from ponds of different ages. Likewise, there is a need for more studies in Eurasia to understand the effect of beaver on C biogeochemistry.

Our goal is to assess consequences of the introduction of alien North American (Castor canadensis (Cc)) beaver into the Nature Reserves inhabited by Eurasian beaver (Castor fiber (Cf)) in European Russia using a mathematical model. For this reason, we have developed a two-species model of population dynamics. Long-term (1934–2015) monitoring data on Cf population dynamics in six Nature Reserves are used in computer modelling of competitive interactions between native Cf and alien Cc. The Reserves are located in the European part of Russia in the north, south, and central part of Cf range. We have simulated the dynamics of both species populations after the introduction of Cc into the habitats occupied by Cf. The model demonstrates that Cf is displaced by Cc in all the Reserves after the introduction of 2 – 24 individuals of Cö. However, the duration of exclusion of one species by the other varies as a function of ecological conditions, initial number of individuals, and fecundities. Our model shows that, in case of introduction of 12 Cc beavers, the size of Cf population starts to decrease after 31–146 years as a result of competition. We study the conditions providing the coexistence of both species and find that Cc population dynamics after Cf exclusion can be described by four patterns: irruptive (Lapland Reserve), single-stage (Prioksko-Terrasny Reserve), multi-stage (Darwin, Central-Forest, and Khoper Reserves) and logistic population growth (Oka Reserve). Species biology in terms of the fecundity, family size, rate of individual development until sexual maturity, life-span, and the age structure of populations are compared between species to detect the mechanisms providing the competitive advantage of Cc over Cf.

Abstract Beavers, primarily through the building of dams, can deliver significant geomorphic modifications and result in changes to nutrient and sediment fluxes. Research is required to understand the implications and possible benefits of widespread beaver reintroduction across Europe. This study surveyed sediment depth, extent and carbon/nitrogen content in a sequence of beaver pond and dam structures in South West England, where a pair of Eurasian beavers (Castor fiber) were introduced to a controlled 1.8 ha site in 2011. Results showed that the 13 beaver ponds, subsequently created, hold a total of 101.53 ± 16.24 t of sediment, equating to a normalised average of 71.40 ± 39.65 kg m2. The ponds also hold 15.90 ± 2.50 t of carbon and 0.91 ± 0.15 t of nitrogen within the accumulated pond sediment. The size of beaver pond appeared to be the main control over sediment storage, with larger ponds holding a greater mass of sediment per unit area. Furthermore, position within the site appeared to play a role with the upper‐middle ponds, nearest to the intensively‐farmed headwaters of the catchment, holding a greater amount of sediment. Carbon and nitrogen concentrations in ponds showed no clear trends, but were significantly higher than in stream bed sediment upstream of the site. We estimate that >70 % of sediment in the ponds is sourced from the intensively managed grassland catchment upstream, with the remainder from in‐situ redistribution by beaver activity. Whilst further research is required into the long term storage and nutrient cycling within beaver ponds, results indicate that beaver ponds may help to mitigate the negative offsite impacts of accelerated soil erosion and diffuse pollution from agriculturally dominated landscapes such as the intensively managed grassland in this study.

The invasion of a species can cause population reduction or extinction of a similar native species due to replacement competition. There is a potential risk that the native Eurasian beaver (Castor fiber) may eventually be competitively excluded by the invasive North American beaver (C. canadensis) from areas where they overlap in Eurasia. Yet currently available methods of census and population estimates are costly and time-consuming. In a laboratory environment, we investigated the potential of using dogs (Canis lupus familiaris) as a conservation tool to determine whether the Eurasian or the North American beaver is present in a specific beaver colony. We hypothesized that dogs can discriminate between the two beaver species, via the odorant signal of castoreum from males and females, in two floor platform experiments. We show that dogs detect scent differences between the two species, both from dead beaver samples and from scent marks collected in the field. Our results suggest that dogs can be used as an “animal biosensor” to discriminate olfactory signals of beaver species, however more tests are needed. Next step should be to test if dogs discern between beaver species in the field under a range of weather conditions and habitat types and use beaver samples collected from areas where the two species share the same habitat. So far, our results show that dogs can be used as a promising tool in the future to promote conservation of the native beaver species and eradication of the invasive one. We therefore conclude that dogs may be an efficient non-invasive tool to help conservationist to manage invasive species in Europe, and advocate for European wildlife agencies to invest in this new tool.

ABSTRACT Beavers are known for their ability to build dams that change the environment. They also occupy territories where they do not construct dams. The goal of this study was to determine which environmental factors influence beaver dam construction and to examine the upstream water level increase caused by the dams. We compared factors collected at 15 beaver territories with dams (32 dams) and 13 territories without dams (i.e., control) in the gently undulating and human-dominated landscape of Middle Belgium in 2013. River width, river depth, distance from woody vegetation, stream velocity, and bank height differed significantly between territories with and without dams. Water depth was the most important parameter to correctly classify territories as either dam territory or control territory (with 97% accuracy). When beavers were present and water depth in summer was <68?cm, the probability of dam building was high; if water depth was >68?cm, dam building was unlikely. Dams caused an increase in the upstream water level of on average 47?±?21?cm. On average the water level could rise only an additional 25?±?30?cm upstream of the dam before bank overtopping would occur. These results provide a simple tool for planners to assess the probability of floodplain inundation by beaver dam building, as part of multifunctional riverine landscape management. ? 2018 The Wildlife Society.

Abstract Increasing air temperatures are changing the arctic tundra biome. Permafrost is thawing, snow duration is decreasing, shrub vegetation is proliferating, and boreal wildlife is encroaching. Here we present evidence of the recent range expansion of North American beaver (Castor canadensis) into the Arctic, and consider how this ecosystem engineer might reshape the landscape, biodiversity, and ecosystem processes. We developed a remote sensing approach that maps formation and disappearance of ponds associated with beaver activity. Since 1999, 56 new beaver pond complexes were identified, indicating that beavers are colonizing a predominantly tundra region (18,293 km2) of northwest Alaska. It is unclear how improved tundra stream habitat, population rebound following over‐trapping for furs, or other factors are contributing to beaver range expansion. We discuss rates and likely routes of tundra beaver colonization, as well as effects on permafrost, stream ice regimes, and freshwater and riparian habitat. Beaver ponds and associated hydrologic changes are thawing permafrost. Pond formation increases winter water temperatures in the pond and downstream, likely creating new and more varied aquatic habitat, but specific biological implications are unknown. Beavers create dynamic wetlands and are agents of disturbance that may enhance ecosystem responses to warming in the Arctic.

Abstract: Rewilding is emerging as a promising restoration strategy to enhance the conservation status of biodiversity and promote self-regulating ecosystems while re-engaging people with nature. Overcoming the challenges in monitoring and reporting rewilding projects would improve its practical implementation and maximize its conservation and restoration outcomes. Here, we present a novel approach for measuring and monitoring progress in rewilding that focuses on the ecological attributes of rewilding. We devised a bi-dimensional framework for assessing the recovery of processes and their natural dynamics through (i) decreasing human forcing on ecological processes and (ii) increasing ecological integrity of ecosystems. The rewilding assessment framework incorporates the reduction of material inputs and outputs associated with human management, as well as the restoration of natural stochasticity and disturbance regimes, landscape connectivity and trophic complexity. Furthermore, we provide a list of potential activities for increasing the ecological integrity after reviewing the evidence for the effectiveness of common restoration actions. For illustration purposes, we apply the framework to three flagship restoration projects in the Netherlands, Switzerland and Argentina. This approach has the potential to broaden the scope of rewilding projects, facilitate sound decision-making and connect the science and practice of rewilding.This article is part of the theme issue ‘Trophic rewilding: consequences for ecosystems under global change’.

Abstract: Ecosystem engineers can increase biodiversity by creating novel habitat supporting species that would otherwise be absent. Their more routine activities further influence the biota occupying engineered habitats. Beavers are well-known for transforming ecosystems through dam building and are therefore increasingly being used for habitat restoration, adaptation to climate extremes and in long-term rewilding. Abandoned beaver ponds (BP) develop into meadows or forested wetlands that differ fundamentally from other terrestrial habitats and thus increase landscape diversity. Active BP, by contrast, are superficially similar to other non-engineered shallow wetlands, but ongoing use and maintenance might affect how BP contribute to aquatic biodiversity. We explored the ‘within-habitat’ effect of an ecosystem engineer by comparing active BP in southern Sweden with coexisting other wetlands (OW), using sedentary (plants) and mobile (water beetles) organisms as indicators. BP differed predictably from OW in environmental characteristics and were more heterogeneous. BP supported more plant species at plot (+15%) and site (+33%) scales, and plant beta diversity, based on turnover between plots, was 17% higher than in OW, contributing to a significantly larger species pool in BP (+17%). Beetles were not differentiated between BP and OW based on diversity measures but were 26% more abundant in BP. Independent of habitat creation beaver are thus significant agents of within-habitat heterogeneity that differentiates BP from other standing water habitat; as an integral component of the rewilding of wetlands re-establishing beaver should benefit aquatic biodiversity across multiple scales.This article is part of the theme issue ‘Trophic rewilding: consequences for ecosystems under global change’.

We evaluated habitat selection by European beaver (Castor fiber L.) across a spatial gradient from local (within the family territory) to a broad, ecoregional scale. Based on aerial photography, we assessed the habitat composition of 150 beaver territories along the main water bodies of the Vistula River delta (northern Poland) and compared these data with 183 randomly selected sites not occupied by the species. The beavers preferred habitats with high availability of woody plants, including shrubs, and avoided anthropogenically modified habitats, such as arable lands. Within a single family territory, we observed decreasing woody plant cover with increasing distance from a colony centre, which suggests that beaver habitat preferences depend on the assessment of both the abundance and spatial distribution of preferred habitat elements. We tested the importance of spatial scale in beaver habitat selection with principal coordinates of neighbour matrices analysis, which showed that the geographical scale explained 46.7% of the variation in habitat composition, while the local beaver density explained only 10.3% of this variability. We found two main spatial gradients that were related to the broad spatial scale: first, the most important gradient was related to the largest distances between beaver sites and was independent of woody plant cover and the local beaver site density. The second most important gradient appeared more locally and was associated with these variables. Our results indicate that European beaver habitat selection was affected by different scale-related phenomena related (1) to central place foraging behaviour, which resulted in the clumped distribution of woody plants within the territory, and (2) local population density and woody plant cover. Finally (3), habitat selection occurs independently across the largest spatial scale studied (e.g., between watersheds), which was probably due to the limited natal dispersal range of the animals.

2017

Abstract: A species’ distribution and abundance in both space and time play a pivotal role in ecology and wildlife management. Collection of such large-scale information typically requires engagement of volunteer citizens and tends to consist of non-repeated surveys made with a survey effort varying over space and time. We here used a hierarchical single-census open population N-mixture model, which was recently developed to handle such challenging census data, to describe the dynamics in the Finnish population sizes of the reintroduced native Eurasian beaver (Castor fiber) and the invasive North American beaver (Castor canadensis). The numbers of beaver winter lodges (i.e., family groups) were counted by volunteers in the municipalities of Finland every third year during 1995?2013. The dynamics of both species followed Gompertz logistic growth with immigration. Initial abundance of North American beavers increased with proximity to the introduction sites as well as with the amount of water in the municipality. The intensively hunted North American beaver population declined and the Eurasian beaver population increased during the study period. The model generated reasonable estimates of both total Finnish and local numbers of lodges, corrected for the incomplete detection. We conclude that the single-census N-mixture model approach has clear potential when using citizen-science data for understanding spatio-temporal dynamics of wild populations.

Abstract: Globally, artificial river impoundment, nutrient enrichment and biodiversity loss impair freshwater ecosystem integrity. Concurrently, beavers, ecosystem engineers recognized for their ability to construct dams and create ponds, are colonizing sites across the Holarctic after widespread extirpation in the 19th century, including areas outside their historical range. This has the potential to profoundly alter hydrology, hydrochemistry and aquatic ecology in both newly colonized and recolonized areas. To further our knowledge of the effects of beaver dams on aquatic environments, we extracted 1366 effect sizes from 89 studies on the impoundment of streams and lakes. Effects were assessed for 16 factors related to hydrogeomorphology, biogeochemistry, ecosystem functioning and biodiversity. Beaver dams affected concentrations of organic carbon in water, mercury in water and biota, sediment conditions and hydrological properties. There were no overall adverse effects caused by beaver dams or ponds on salmonid fish. Age was an important determinant of effect magnitude. While young ponds were a source of phosphorus, there was a tendency for phosphorus retention in older systems. Young ponds were a source methylmercury in water, but old ponds were not. To provide additional context, we also evaluated similarities and differences between environmental effects of beaver-constructed and artificial dams (767 effect sizes from 75 studies). Both are comparable in terms of effects on, for example, biodiversity, but have contrasting effects on nutrient retention and mercury. These results are important for assessing the role of beavers in enhancing and/or degrading ecological integrity in changing Holarctic freshwater systems.

Abstract: Potential for habitat restoration is increasingly used as an argument for reintroducing ecosystem engineers. Beaver have well known effects on hydromorphology through dam construction, but their scope to restore wetland biodiversity in areas degraded by agriculture is largely inferred. Our study presents the first formal monitoring of a planned beaver-assisted restoration, focussing on changes in vegetation over 12years within an agriculturally-degraded fen following beaver release, based on repeated sampling of fixed plots. Effects are compared to ungrazed exclosures which allowed the wider influence of waterlogging to be separated from disturbance through tree felling and herbivory. After 12years of beaver presence mean plant species richness had increased on average by 46% per plot, whilst the cumulative number of species recorded increased on average by 148%. Heterogeneity, measured by dissimilarity of plot composition, increased on average by 71%. Plants associated with high moisture and light conditions increased significantly in coverage, whereas species indicative of high nitrogen decreased. Areas exposed to both grazing and waterlogging generally showed the most pronounced change in composition, with effects of grazing seemingly additive, but secondary, to those of waterlogging. Our study illustrates that a well-known ecosystem engineer, the beaver, can with time transform agricultural land into a comparatively species-rich and heterogeneous wetland environment, thus meeting common restoration objectives. This offers a passive but innovative solution to the problems of wetland habitat loss that complements the value of beavers for water or sediment storage and flow attenuation. The role of larger herbivores has been significantly overlooked in our understanding of freshwater ecosystem function; the use of such species may yet emerge as the missing ingredient in successful restoration.

Abstract: The construction of beaver dams facilitates a suite of hydrologic, hydraulic, geomorphic, and ecological feedbacks that increase stream complexity and channel–floodplain connectivity that benefit aquatic and terrestrial biota. Depending on where beaver build dams within a drainage network, they impact lateral and longitudinal connectivity by introducing roughness elements that fundamentally change the timing, delivery, and storage of water, sediment, nutrients, and organic matter. While the local effects of beaver dams on streams are well understood, broader coverage network models that predict where beaver dams can be built and highlight their impacts on connectivity across diverse drainage networks are lacking. Here we present a capacity model to assess the limits of riverscapes to support dam-building activities by beaver across physiographically diverse landscapes. We estimated dam capacity with freely and nationally-available inputs to evaluate seven lines of evidence: (1) reliable water source, (2) riparian vegetation conducive to foraging and dam building, (3) vegetation within 100m of edge of stream to support expansion of dam complexes and maintain large colonies, (4) likelihood that channel-spanning dams could be built during low flows, (5) the likelihood that a beaver dam is likely to withstand typical floods, (6) a suitable stream gradient that is neither too low to limit dam density nor too high to preclude the building or persistence of dams, and (7) a suitable river that is not too large to restrict dam building or persistence. Fuzzy inference systems were used to combine these controlling factors in a framework that explicitly also accounts for model uncertainty. The model was run for 40,561km of streams in Utah, USA, and portions of surrounding states, predicting an overall network capacity of 356,294 dams at an average capacity of 8.8dams/km. We validated model performance using 2852 observed dams across 1947km of streams. The model showed excellent agreement with observed dam densities where beaver dams were present. Model performance was spatially coherent and logical, with electivity indices that effectively segregated capacity categories. That is, beaver dams were not found where the model predicted no dams could be supported, beaver avoided segments that were predicted to support rare or occasional densities, and beaver preferentially occupied and built dams in areas predicted to have pervasive dam densities. The resulting spatially explicit reach-scale (250m long reaches) data identifies where dam-building activity is sustainable, and at what densities dams can occur across a landscape. As such, model outputs can be used to determine where channel–floodplain and wetland connectivity are likely to persist or expand by promoting increases in beaver dam densities.

Abstract: As dispersal is a dangerous part of an individual’s life, its timing is important to increase the chances of survival and successful establishment of a territory. We investigated factors affecting the timing of natal dispersal in the Eurasian beaver, Castor fiber, a territorial, monogamous, long-lived mammal, using data from an 18-year individual-based study (1998-2015). We tested hypotheses about the causes of dispersal onset, namely competitive ability, kin competition (sibling competition and offspring parent competition), population density and intolerance by an incoming, unrelated dominant individual. Only 9% of individuals remained philopatric and became dominant after both of their parents disappeared. Average age at dispersal was 3.5 years, with some individuals delaying dispersal up to age 7 years. Beavers dispersed more frequently with increasing age (i.e. with increasing competitive ability and possibly experience) and when population density was lower. Further, both females and males delayed dispersal with increasing same-sex parental age. Older parents were either more tolerant towards philopatric subordinates, or subordinates awaited the disappearance of their senescing parents to take over the natal territory. From comparisons with other populations, we conclude that the high population density in our area was possibly the ultimate driver of dispersal with individuals delaying dispersal to increase their competitive ability.

Abstract: Basic information on patterns and correlates of growth and reproduction are essential for understanding a species’ life history strategy. For the Eurasian beaver (Castor fiber), knowledge of life history is fragmentary and correlates of growth and reproduction unstudied. We related measures of somatic fitness including growth rate, body size (length), body condition (fat) and body mass to measures of reproductive investment including fecundity (number of corpora lutea (CL) and fetuses), age-specific reproduction, age of primiparity and parturition date in 59 female beavers culled from mid-March to mid-May in south-east Norway. Increase in body length ceased after age three. Primiparity at ages two and three was related to body length and mass, but not fat. Postponed primiparity beyond age two was common. Fecundity was significantly higher in fatter individuals and showed a trend to increase with age. For females ≥age three, those pregnant were significantly fatter than barren individuals. Intermittent years of non-breeding were common among sexually mature females. The mean number of CL and fetuses alive at the females time of death among 32 pregnant individuals was 3.0 ± 0.9 (range 1–6) and 2.3 ± 0.9 (range 1–4) respectively. Females conceiving at the normal peak time in late January were significantly heavier than individuals that conceived 1–3 months later. Late breeders, however, had significantly more CL, possibly because the improved nutrient levels provided by early spring growth led to higher ovulation rates. Fat accumulated during summer and autumn prior to winter breeding appears to be an important determinant of reproduction in female beavers.

Abstract: Beavers are the archetypal keystone species, which can profoundly alter ecosystem structure and function through their
ecosystem engineering activity, most notably the building of dams. This can have a major impact upon water resource
management, flow regimes and water quality. Previous research has predominantly focused on the activities of North
American beaver (Castor canadensis) located in very different environments, to the intensive lowland agricultural landscapes
of the United Kingdom and elsewhere in Europe.

Two Eurasian beavers (Castor fiber) were introduced to a wooded site, situated on a first order tributary, draining from intensively managed grassland. The site was monitored to understand impacts upon water storage, flow regimes and water quality. Results indicated that beaver activity, primarily via the creation of 13 dams, has increased water storage within the site (holding ca. 1000 m3 in beaver ponds) and beavers were likely to have had a significant flow attenuation impact, as determined from peak discharges (mean 30 ± 19% reduction), total discharges (mean 34 ± 9% reduction) and peak rainfall to peak discharge lag times (mean 29 ± 21% increase) during storm events. Event monitoring of water entering and leaving the site showed lower concentrations of suspended sediment, nitrogen and phosphate leaving the site (e.g. for suspended sediment; average entering site: 112 ± 72 mg l− 1, average leaving site: 39 ± 37 mg l− 1). Combined with attenuated flows, this resulted in lower diffuse pollutant loads in water downstream. Conversely, dissolved organic carbon concentrations and loads downstream were higher. These observed changes are argued to be directly attributable to beaver activity at the site which has created a diverse wetland  environment, reducing downstream hydrological connectivity. Results have important implications for beaver reintroduction programs which may provide nature based solutions to the catchment-scale water resource management issues that are faced in agricultural landscapes.

Abstract: Species Distribution Models (SDMs) may provide important information for the follow-up phase of reintroduction operations by identifying the main areas most likely to be colonized by the reintroduced species. We used SDMs to identify the potential distribution of Eurasian beavers (Castor fiber) reintroduced to Serbia and Bosnia and Herzegovina in 2004–2006 after being historically driven to extinction by overhunting. Models were also used to carry out a gap analysis to assess the degree of protection granted by the national reserve networks to the potentially expanding population. Distances from hydrographic network, broadleaved forest, main watercourses and farmland were the main factors influencing model performance. We estimated that suitable habitat covers 14.0% (31,000km2) of the whole study area. In Serbia, in 2004–2013 beavers expanded their range at a mean colonization speed of 70.9±12.8km/year (mean±SD). Only 2.89% of and 9.72% of beaver’s suitable habitat lie within the national network of protected areas of Bosnia and Serbia respectively. We detected new potential areas where beavers will likely settle in the near future, advising on where further monitoring should be carried out. We also identified low suitability areas to be targeted with appropriate management to improve their conditions as well as important regions falling outside reserve boundaries to which protection should be granted.

Abstract: Many vertebrate scavengers function as predators in ecosystems, suggesting that the presence of scavengers and occurrence of predator effects may be intertwined near carcasses. We tested for risk effects near a series of experimentally placed carcasses by measuring small-mammal foraging in a before–after control–impact design. Validation efforts revealed low levels of food loss from stations due to human error and invertebrate foraging, and habituation to stations occurred after 2 weeks. Increased perceived predation risk by small mammals relative to controls occurred in three of seven trials. The effect was observed across tested carcass types (beaver, Castor canadensis Kuhl, 1820; white-tailed deer, Odocoileus virginianus (Zimmermann, 1780)) and seasons (summer and fall). However, small mammals also increased foraging relative to controls in two of seven trials, and foraging reached a ceiling in two other trials that prevented inference on a response. Taken together, our results suggest that scavenger recruitment to carcasses can in some instances create islands of risk for prey on the landscape, but the effect is not likely to be universal. Where small-mammal foraging does decrease, further work will be necessary to determine if risk effects cascade to adjacent trophic levels through enhanced seed and seedling survival.

Abstract: The North American beaver (Castor canadensis) is an invasive species in southern Patagonia, introduced in 1946 as part of a program by the Argentine government to augment furbearers. Research focus has turned from inventorying the beaver’s population and ecosystem impacts toward eradicating it from the region and restoring degraded areas. Successful restoration, however, requires a fuller determination of how beavers have altered physical landscape characteristics, and of what landscape features and biota need to be restored. Our goal was to identify changes to the physical landscape by invasive beaver. We analyzed channel and valley morphology in detail at one site in each of the three major forest zones occurring on the Argentine side of Tierra del Fuego’s main island. We also assessed 48 additional sites across the three forest biomes on the island to identify a broader range of aquatic habitat occupied and modified by beaver. Beaver build dams with Nothofagus tree branches on streams, which triggered mineral sediment accretion processes in the riparian zone, but not in ways consistent with the beaver meadow theory and only at a few sites. At the majority of sites, beavers actively excavated peat and mineral sediment, moved thousands of cubic meters of sediment within their occupied landscapes and used it to build dams. Beaver were also common in fen ecosystems where pond formation inundated and drowned peat forming mosses and sedges, and triggered a massive invasion of exotic plant species. Results highlight that restoration of fen ecosystems is a previously unrecognized but pressing and challenging restoration need in addition to reforestation of Nothofagus riparian forests. We recommend that decision-makers include the full ecosystem diversity of the Fuegian landscape in their beaver eradication and ecosystem restoration plans.

2016

Abstract: * Predators affect prey populations not only through direct predation, but also by acting as definitive hosts for their parasites and completing parasite life cycles. Understanding the affects of parasitism on prey population dynamics requires knowing how their predators’ parasite community is affected by diet and prey availability. Ungulates, such as moose (Alces americanus) and white-tailed deer (Odocoileus virginianus), are often important prey for wolves (Canis lupus), but wolves also consume a variety of alternative prey, including beaver (Castor canadensis) and snowshoe hare (Lepus americanus). * The use of alternative prey, which may host different or fewer parasites than ungulates, could potentially reduce overall abundance of ungulate parasites within the ecosystem, benefiting both wolves and ungulate hosts. * We examined parasites in wolf carcasses from eastern Manitoba and estimated wolf diet using stable isotope analysis. Taeniidae cestodes were present in most wolves (75%), reflecting a diet primarily comprised of ungulates, but nematodes were unexpectedly rare. * Cestode abundance was negatively related to the wolf’s ?13C value, indicating diet affects parasite abundance. Wolves that consumed a higher proportion of beaver and caribou (Rangifer tarandus), estimated using Bayesian mixing models, had lower cestode abundance, suggesting the use of these alternative prey can reduce parasite loads. * Long-term consumption of beavers may lower the abundance of adult parasites in wolves, eventually lowering parasite density in the region and ultimately benefiting ungulates that serve as intermediate hosts. Thus, alternative prey can affect both predator-prey and host-parasite interactions and potentially affect food web dynamics.

Abstract: According to optimal foraging theory, consumers make choices that maximize their net energy intake per unit of time. We used foraging theory as a framework to understand the foraging behaviour of North American beavers (Castor canadensis Kuhl, 1820), an important herbivore that engineers new habitats. We tested the hypothesis that beavers are energy maximizers by verifying the prediction that they allocate time to foraging activities independently of habitat quality in Kouchibouguac National Park of Canada in New Brunswick, where nearly five decades of unabated colonization by beavers led to family units established in habitats of varying quality. We observed the behaviour of 27 beavers at seven ponds from May to August 2001, at dusk and dawn. Habitat quality did not influence time that beavers allocated to foraging. This finding supported our hypothesis. The only factor in the best model explaining time spent foraging was the progression of spring and summer seasons (weekly periods). Limiting factors such as infrastructure maintenance and intermittent reactions to danger remain poorly understood for this important herbivore. Future research should focus on establishing the importance that habitat quality (food availability) and environmental stress (weather, predators) have on shaping its time budget and, consequently, its survival and reproductive success.

Abstract: Beaver (Castor sp.) can change the riverine environment through dam-building and other activities. The European beaver (Castor fiber) was extirpated in Poland by the nineteenth century, but populations are again present as a result of reintroductions that began in 1974. The goal of this paper is to assess the impact of beaver activity on montane fluvial system development by identifying and analysing changes in channel and valley morphology following expansion of beaver into a 7.5km-long headwater reach of the upper Wisłoka River in southeast Poland. We document the distribution of beaver in the reach, the change in river profile, sedimentation type and storage in beaver ponds, and assess how beaver dams and ponds have altered channel and valley bottom morphology. The upper Wisłoka River fluvial system underwent a series of anthropogenic disturbances during the last few centuries. The rapid spread of C. fiber in the upper Wisłoka River valley was promoted by the valley’s morphology, including a low-gradient channel and silty-sand deposits in the valley bottom. At the time of our survey (2011), beaver ponds occupied 17% of the length of the study reach channel. Two types of beaver dams were noted: in-channel dams and valley-wide dams. The primary effect of dams, investigated in an intensively studied 300-m long subreach (Radocyna Pond), was a change in the longitudinal profile from smooth to stepped, a local reduction of the water surface slope, and an increase in the variability of both the thalweg profile and surface water depths. We estimate the current rate of sedimentation in beaver ponds to be about 14cm per year. A three-stage scheme of fluvial processes in the longitudinal and transverse profile of the river channel is proposed. C. fiber reintroduction may be considered as another important stage of the upper Wisłoka fluvial system development.

Abstract: Territoriality is only profitable when the benefits gained from territory exploitation exceed the costs of defence, and territory sizes are usually optimized by time constraints related to resource defence (e.g. patrolling) and exploitation. In this study, we equipped 25 dominant Eurasian beavers (Castor fiber) with GPS units to study spatial movement patterns both on land and in water in relation to territory size, resource availability, the number of neighbours, season, and the beavers’ age. We show a territory size-dependent trade-off between territorial behaviours and foraging distances: Beavers in larger territories moved greater distances each night, thereby spending more time patrolling, and stayed closer to the shoreline when being on land (i.e. when foraging). Inversely, in smaller territories beavers patrolled less and foraged further away from the shoreline. These results suggest that individuals trade-off the costs of patrolling larger territories against the benefits of foraging closer towards the shoreline. Smaller territories might be more prone to resource depletion, thus, making foraging further from the shoreline a strategy to ensure sustainable resource use. Further, older beavers spent more time on land and close to territory borders compared to younger ones, suggesting a behavioural change with age possibly due to increased experience and boldness.

Abstract: * Small-scale discontinuities, formed by accumulations of wood, are recognised as a key feature of functionally intact forested streams because they promote organic matter retention, increase habitat complexity and provide flow refugia. Re-establishing such features in physically degraded streams is therefore a common priority for restoration schemes. Ecosystem engineering by beavers in the form of dam building might offer a natural mechanism for restoring degraded streams. Despite an increase in beaver reintroductions globally, the ecosystem engineering concept has rarely been applied to restoring biodiversity and ecosystem function, especially within degraded freshwater systems.* By comparing multiple beaver-modified and unmodified sites on headwater streams draining 13 ha of pastureland in eastern Scotland, U.K., we investigated if hydromorphological changes caused by reintroduced beavers (Castor fiber) translate into desirable biological responses when there is a long history of physical degradation and contraction of the regional species pool due to agricultural land use. * Beaver modified in-stream habitat by constructing 10 dams, thus creating a series of interconnected dam pools. Organic matter retention and aquatic plant biomass increased (7 and 20 fold higher respectively) in beaver ponds relative to unmodified channels, consistent with the lower fluctuation in stream stage observed below a series of dams. Growing season concentrations of extractable P and NO3 were on average 49% and 43% lower respectively below a series of dams than above, although colour and suspended solids concentrations increased. * Macroinvertebrate samples from beaver-modified habitats were less taxon rich (alpha diversity on average 27% lower) than those from unmodified stream habitat. However, due to significant compositional differences between beaver versus unmodified habitats, a composite sample from all habitats indicated increased richness at the landscape scale; gamma diversity was 28% higher on average than in the absence of beaver-modified habitat. Feeding guild composition shifted from grazer/scraper and filter feeder dominance in unmodified habitats to shredder and collector-gatherer dominance in beaver-created habitats. * Dam building by beaver in degraded environments can improve physical and biological diversity when viewed at a scale encompassing both modified and unmodified habitats. By restoring ecosystem processes locally, it may also offer wider scale benefits, including greater nutrient retention and flood attenuation. These benefits should be evaluated against evidence of any negative effects on land use or fisheries.

Abstract: * The occurrence and importance of fluxes of nutrients and organic matter between aquatic and terrestrial habitats is well established, but how catchment characteristics influence these fluxes remains unclear. Beaver (Castor canadensis) alter freshwater ecosystems and increase aquatic production, but it is unknown how these changes influence the magnitude and lateral dispersal of aquatic nutrients into terrestrial ecosystems.

* We examined differences in abundances of dominant aquatic invertebrates, wolf spiders (Lycosidae), and deer mice (Peromyscus maniculatus), at beaver and non-beaver sites. We used stable isotopes to track aquatic-derived carbon in terrestrial consumers and linear mixed-effects models to examine the importance of beaver presence and distance from stream channel on the percentage of aquatic-derived carbon in terrestrial consumers.

* Sites with beaver activity had >200% higher aquatic invertebrate emergence rates as well as 60% and 75% higher abundances of spiders and deer mice, respectively, relative to non-beaver sites.

* The tissues of both spiders and deer mice exhibited a greater percentage of aquatic-derived carbon at sites with beaver activity than at non-beaver sites.

* Aquatic-derived carbon in deer mice declined linearly with distance from the stream edge at both beaver and non-beaver sites. The contribution of aquatic-derived carbon in mice extended farther from the stream edge in beaver-modified catchments. Aquatic-derived carbon in spiders also declined linearly with distance from the stream at beaver sites but not at non-beaver sites.

* We documented a novel example of increased aquatic subsidy to riparian areas with beaver activity, leading to changes in the magnitude of the lateral dispersal of aquatic nutrient subsidies to the terrestrial environment in small stream systems. Understanding the effects of natural disturbance regimes, such as beaver modification, will be important for management and, where appropriate, restoration of natural catchment processes.

Abstract: The North American beaver (Castor canadensis) builds dams that pond water on streams, which provide crucial ecological services to aquatic and riparian ecosystems and enhance biodiversity. Consequently, there is increasing interest in restoring beavers to locations where they historically occurred, particularly in the arid western United States. However, despite often intensive efforts to reintroduce beavers into areas where they were severely reduced in numbers or eliminated due to overharvesting in the eighteenth and nineteenth centuries, beavers remain sparse or missing from many stream reaches. Reasons for this failure have not been well studied. Our goal was to evaluate certain biotic factors that may limit the occurrence of dam-building beavers in northern New Mexico, including competitors and availability of summer and winter forage. We compared these factors at primary active dams and at control sites located in stream reaches that were physically suitable for dam-building beavers but where none occurred. Beaver dams mostly occurred at sites that were not grazed or where there was some alternative grazing management, but were mostly absent at sites within Forest Service cattle allotments. Results indicated that cattle grazing influenced the relation between vegetation variables and beaver presence. The availability of willows (Salix spp.) was the most important plant variable for the presence of beaver dams. We conclude that grazing by cattle as currently practiced on Forest Service allotments disrupts the beaver-willow mutualism, rendering stream reaches unsuitable for dam-building beavers. We recommend that beaver restoration will require changes to current livestock management practices.

Abstract: One key assumption often inferred with using radio-equipped individuals is that the transmitter has no effect on the metric of interest. To evaluate this assumption, we used a known fate model to assess the effect of transmitter type (i.e., tail-mounted or peritoneal implant) on short-term (1 yr) survival and a joint live-dead recovery model and results from a mark-recapture study to compare long-term (8 yr) survival and body condition of ear-tagged only American beavers (Castor canadensis) to those equipped with radio transmitters in Voyageurs National Park, Minnesota, USA. Short-term (1-yr) survival was not influenced by transmitter type (wi = 0.64). Over the 8-yr study period, annual survival was similar between transmitter-equipped beavers (tail-mounted and implant transmitters combined; 0.76; 95% CI = 0.45-0.91) vs ear-tagged only (0.78; 95% CI = 0.45-0.93). Additionally, we found no difference in weight gain (t9 = 0.25, P = 0.80) or tail area (t11 = 1.25, P = 0.24) from spring to summer between the two groups. In contrast, winter weight loss (t22 = ?2.03, p = 0.05) and tail area decrease (t30 = ?3.04, p = 0.01) was greater for transmitter-equipped (weight = ?3.09 kg, SE = 0.55; tail area = ?33.71 cm2, SE = 4.80) than ear-tagged only (weight = ?1.80 kg, SE = 0.33; tail area = ?12.38 cm2, SE = 5.13) beavers. Our results generally support the continued use of transmitters on beavers for estimating demographic parameters, although we recommend additional assessments of transmitter effects under different environmental conditions.

Abstract: * In Scotland, UK, beavers became extinct about 400 years ago. Currently, two wild populations are present in Scotland on a trial basis, and the case for their full reintroduction is currently being considered by Scottish ministers. Beavers are widely considered “ecosystem engineers”. Indeed, beavers have large impacts on the environment, fundamentally change ecosystems, and create unusual habitats, often considered unique. In this review, we investigate the mechanisms by which beavers act as ecosystem engineers, and then discuss the possible impacts of beavers on the biodiversity of Scotland.
* A meta-analysis of published studies on beavers’ interactions with biodiversity was conducted, and the balance of positive and negative interactions with plants, invertebrates, amphibians, reptiles, birds, and mammals recorded.
* The meta-analysis showed that, overall, beavers have an overwhelmingly positive influence on biodiversity. Beavers’ ability to modify the environment means that they fundamentally increase habitat heterogeneity. As beavers are central-place foragers that feed only in close proximity to watercourses, their herbivory is unevenly spread in the landscape. In addition, beaver ponds and their associated unique successional stages increase habitat heterogeneity both spatially and temporally. Beavers also influence the ecosystems through the creation of a variety of features such as dams and lodges, important habitat features such as standing dead wood (after inundation), an increase in woody debris, and a graded edge between terrestrial and aquatic habitats that is rich in structural complexity.
* In Scotland, a widespread positive influence on biodiversity is expected, if beavers are widely reintroduced. For instance, beaver activity should provide important habitat for the otter Lutra lutra, great crested newt Triturus cristatus and water vole Arvicola amphibious, all species of conservation importance.
* Beavers are most likely to have detrimental impacts on certain woodland habitats and species of conservation importance, such as the Atlantic hazelwood climax community and aspen Populus tremula woodland. A lack of woodland regeneration caused by high deer abundance could lead to habitat degradation or loss. These are also of particular importance due to the variety of associated dependent species of conservation interest, such as lichen communities in Atlantic hazelwoods.

Abstract: Deadwood is a markedly important ecosystem element, and increasingly rare in managed landscapes. Beavers (Castor sp.) are ecosystem engineers of the boreal forest, where they modify riparian forests and wetlands through damming. The subsequent inundation causes extensive die-off of trees in the flood zone. We measured the deadwood volumes and types for six beaver-created flood sites, and compared these to control sites with no beaver influence. Our results show beavers create abundant volumes of deadwood in areas rarely experiencing other disturbance types. Significant amounts of beaver-created deadwood consist of rare types, e.g. snags and deciduous wood. Both coarse and fine woody debris are created. These varying substrates increase deadwood heterogeneity and create differing saproxylic community diversity compared to other disturbances. The roaming lifestyle of beavers cause repeated flooding in boreal landscapes. This upholds deadwood continuity in areas where deadwood levels are very low due to intensive forest management. The reoccurring pulses of deadwood created by beavers may facilitate a wide scope of deadwood-dependent species. The beaver can be used as a deadwood facilitator and engine of restoration in boreal wetlands and riparian forests. This is an economic option compared to costly and time-consuming man-made restoration.

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