Beavers
Beavers are large (15 – 38 kg in weight), semi-aquatic rodents that live in rivers, streams, ditches, lakes and wetland areas. At one time they were widespread and common in Europe, but by 1900 they had been lost from large parts of their native range, including the United Kingdom, as a result of over-hunting and habitat loss. Since then, however, they have returned to much of their former range through regulation of hunting, translocations, reintroductions, and natural processes. A parallel situation has occurred with the Canadian beaver (C. canadensis) in North America. Some characteristics of beavers are shown in Table 1; these will be discussed in the following pages of the website. Table 2 summarises some of the key differences between the Eurasian beaver and the Canadian beaver. Canadian beavers have been introduced into Europe and can still be found in some places.
Table 1 Some characteristics of beavers (from Gurnell et al. 2008, based on
Müller-Schwarze & Sun 2003, Cole et al. 2007)
| Feature | Description |
|---|---|
| . | . |
| International status of European beavers | Bern Convention (Convention on the Conservation of European Natural and Wildlife Habitats, Appendix III |
| Conservation on Natural Habitats of Wild Fauna and Flora, Annexes II and IV (not including Swedish and Finnish beaver which are Annex V) | |
| Chromosomes | European beaver 2n = 48, Canadian beaver, 2n = 40 |
| Density | 0.2 – 0.6 beaver pairs per km^2 |
| Dispersal | Usually when 1 to 2 years old; maximum distance 170 km, median 25 km |
| Use of space | Territorial |
| Social group | Adult pair plus young of year (kits), and possibly young of previous year (yearlings), average number of animals ~4. |
| Life span and survival | Can live 7-8 years; high mortality when <6 months old and during dispersal. |
| Breeding system | Obligate monogamy; monoestrous; average litter size 1.9-3.1 young European beaver, 3.2-4.7 Canadian beaver; gestation 105 days; suckling 60-90 days; births peak in May/June. Mature at 2 years old, first breed at 3 years old. Young precocious, fully furred and with open eyes at birth |
| Dam building | More sophisticated and developed in Canadian beaver than European beaver |
| Dens or lodges | European beaver prefer lodges or burrows in riverbank with entrance below water level. Lodges may be built out of woody debris, twigs and soil where bank burrows are not possible. Canadian beaver also construct freestanding lodges |
| Scent-marking | Scent mounds marked with spray from castor glands, or secretions from anal glands by anal dragging – can be much larger in Canadian beavers |
| Warning sound | Tail slap on surface of water |
| Activity | Crepsucular and nocturnal, all year |
| Diet | Herbivores, mainly herbs from spring to summer, and wood bark during autumn and winter – aspen, willow, poplar, alder preffered. Central place foragers with most feeding closest to lodge, and within 20 m of river margin. Digs feeding channels. Caches food under water near den during winter. |
Table 2 Some differences between Eurasian and Canadian or North American beavers
(based on Müller-Schwarze 2011)
| Feature | Eurasian beaver | Canadin beaver |
|---|---|---|
| Body size | Older animals lightly smaller | Older animals lightly larger |
| Skull:nasal opening | Triangular | Square |
| Skull:volume | Smaller | Larger |
| Womb | Present | Absent |
| Tail size | Narrower: width ~40% of length | Wider: width ~56% of length |
| Tail vertebae | Narrw; processes less developed | Wider: processes more developed |
| Anal gland secretion | Darker in females | Darker in males |
| Average litter size | 1.9 to 3.1 | 3.2 to 4.7 |
| Resistance to tularemia, a serious infectious bacterial disease | Strong | Weak |
| Internal helminth, Travassosius rufus | Not found in Europe | Prevalent |
| Beaver beetle. Leptinillus validus | Absent | Present |
| Dam building | Less developed | Sophisticated |
| Lodges | Mostly in bank | Many freestanding |
| Scent mounds | Smaller | Larger; some ‘giants’ |