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)

FeatureDescription
..
International status of European beaversBern 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)
ChromosomesEuropean beaver 2n = 48, Canadian beaver, 2n = 40
Density0.2 - 0.6 beaver pairs per km^2
DispersalUsually when 1 to 2 years old; maximum distance 170 km, median 25 km
Use of spaceTerritorial
Social groupAdult pair plus young of year (kits), and possibly young of previous year (yearlings), average number of animals ~4.
Life span and survivalCan live 7-8 years; high mortality when <6 months old and during dispersal.
Breeding systemObligate 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 buildingMore sophisticated and developed in Canadian beaver than European beaver
Dens or lodgesEuropean 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-markingScent mounds marked with spray from castor glands, or secretions from anal glands by anal dragging - can be much larger in Canadian beavers
Warning soundTail slap on surface of water
ActivityCrepsucular and nocturnal, all year
DietHerbivores, 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)

FeatureEurasian beaverCanadin beaver
Body sizeOlder animals lightly smallerOlder animals lightly larger
Skull:nasal openingTriangularSquare
Skull:volumeSmallerLarger
WombPresentAbsent
Tail sizeNarrower: width ~40% of lengthWider: width ~56% of length
Tail vertebaeNarrw; processes less developedWider: processes more developed
Anal gland secretionDarker in femalesDarker in males
Average litter size1.9 to 3.13.2 to 4.7
Resistance to tularemia, a serious infectious bacterial diseaseStrongWeak
Internal helminth, Travassosius rufusNot found in EuropePrevalent
Beaver beetle. Leptinillus validusAbsentPresent
Dam buildingLess developedSophisticated
LodgesMostly in bankMany freestanding
Scent moundsSmallerLarger; some 'giants'