Castor fiber, Linnaeus, 1758

Don E. Wilson, Thomas E. Lacher, Jr & Russell A. Mittermeier, 2016, Castoridae, Handbook of the Mammals of the World – Volume 6 Lagomorphs and Rodents I, Barcelona: Lynx Edicions, pp. 150-168 : 166-167

1.

Eurasian

Beaver

Castor fiber

French: Castor d'Europe / German: Eurasischer Biber / Spanish: Castor euroasiatico

Other common names: European Beaver

Taxonomy. Castor fiber Linnaeus, 1758 ,

“Habitat in Europa, Afiee, Americ.”

Eight subspecies have been recognized based on geography and morphological differences. However, recent analysis of both mtDNA and nDNA suggests that there are only two phlyogroups, a western and an eastern group, and neither can be considered a separate subspecies. Monotypic.

Distribution. N, C & E Europe, from Scandinavia and Russia to S France (Rhone Delta), extensive and small isolated populations in W & C Siberia, and in the Amur Basin, Russian Far East, and small relic populations in the Altai region of SW Mongolia and NWChina.

Descriptive notes. Head—body 800-900 mm, tail 200-300 mm; weight 15-20 kg (rarely, 30-40 kg). Eurasian Beavers are the second largest rodent species (tied with the North American Beaver, C. canadensis ) and the largest European rodent. There is no physical sexual dimorphism. Eurasian Beavers are stocky, robust rodents with relatively massive skeletons. Fronts of incisors are reddish-orange, caused byiron concentration for strength. Coat color ranges from light brown to darker reddish-brown to almost black; brownish color is most common. Eurasian Beavers have long guard hairs and dense underfur. Many other physical adaptations are associated with their aquatic habits. Eurasian Beavers have small forelimbs and hands, with powerful digging claws, and webbed hindfeet. Ears and nose can close; eyes have a membrane that covers them when diving. Tail is prominent and dorsal-ventrally flattened, and it can be more or less oval-shaped depending on geographical location.

Habitat. Associated with all types of freshwater wetlands, from large rivers to small streams, lakes, and ponds, and also along wetland systems associated with agricultural land such as irrigation canals and fishponds. Eurasian Beavers are most closely associated with wetlands that contain species in the family Salicaceae (e.g. willows, Salix spp. , and aspens and poplars, both Populus spp. ), but theyare also found in areas that lack these species. They also use ponds and lakes that contain water lilies ( Nuphar spp. and Nymphaea spp. , Nymphaeaceae ), which might be related to sodium availability. Eurasian Beavers are found from lowland areas to mountainous regions; in mountain areas, stream gradient limits colonization. They can tolerate human activity and are found living in large rivers in cities (e.g. Vienna) and on rivers with industrial sites (e.g. Switzerland). Widths of riparian borders along streams and rivers are probably associated with habitat use.

Food and Feeding. Eurasian Beavers eat a variety ofriparian woody and herbaceous plants. They are generalist herbivores but can be highly specialization in their food selection. They prefer willows and aspens but also eat other deciduous species including maples (Acer spp., Aceraceae ); alders ( Alnus spp. ) and birches ( Betula spp. , both Betulaceae ); and oaks ( Quercus spp. , Fagaceae ). They might seasonally eat evergreens such as pines ( Pinus spp. ), firs ( Abies spp. ), and hemlocks (7suga spp., all Pinaceae ). They also seasonally eat many species of herbaceous plants. Eurasian Beavers take trees that are much larger than theyare as food items, but they primarily eat branches, bark with associated cambium layer, and leaves. They have associated gut micro-biota that helps with some cellulose digestion. Cutting of trees and woody vegetation is most pronounced in autumn but can occur in all seasons. Across their distribution, Eurasian Beavers build food caches of branches in autumn that they eat during winter—variable depending on geographical location. Although they use most riparian species, woody and herbaceous, they concentrate on a few species, to some degree, for the majority oftheir diet.

Breeding. Eurasian Beavers breed once a year, and females come into estrus in December-May, with a peak in January-February. Estrus lasts 12-24 hours, and iffertilization does not occur, females come into estrus again. Gestation is 100-110 days, and young are born in spring or early summer. Litter size is 1-6 young but averages 2. Males and females become reproductively active at 2-3 years of age. Eurasian Beavers are socially monogamous if not genetically monogamous, and form pair bonds thatlast for years. Rarely, multiple pregnant females have been reported in one family group. Copulation might occur in the water or in the lodge or burrow. Eurasian Beavers live 8-15 years in the wild—relatively long for a rodent.

Activity patterns. Eurasian Beavers are nocturnal, becoming active in the evening (17:00-19:00 h) and remaining active until morning (06:00-08:00 h). They might return to their daytime rest site (lodge or burrow) many times during an activity period. When active, theypatrol their territory, swim, feed, and groom. Interactions with other family members do occur, most often among adults and young. In autumn, they are active cutting woody vegetation, building a food cache, and putting mud and branches on their lodges.

Movements, Home range and Social organization. Eurasian Beavers live in family groups (a mated pair of adults, young-of-the-year, and yearlings). They are territorial and mark territorial boundaries with scent mounds. They move within their territories and might even move between territories in spring and summer. Movements tend to be only a few hundred meters. Two-year-old Eurasian Beavers generally disperse from their natal areas in spring, summer, or autumn. These movements average 5-10 km but might be longer depending on quality ofavailable habitat and density of the population. There is some indication that females disperse farther than males, but this might not be consistent. Home ranges are usually represented as linear lengths of shoreline occupied and are 0-5-1-5 km. Eurasian Beavers tend to forage within 30 m of the shoreline, although forays of 100 m or more are observed. Movements within a territory are dependent of habitat quality. Adults are dominant to young individuals within a family, and no consistent dominance of one sex over the other has been documented. There is evidence that Eurasian Beavers recognize anal gland secretions or castoreum scents oftheir family members and nearest neighbors more than less familiar individuals and react more strongly to unfamiliar scent.

Status and Conservation. Classified as Least Concern on The IUCN Red List. The Eurasian Beaver has come back from near extinction across its distribution due to conservation efforts, hunting bans, and active reintroduction programs. It was regionally extinct by the end of the 19" century and existed in small populations in isolated refugia in Central Europe, Norway, and Russia. From an estimated 1200 individuals in the early 1900s, the Eurasian Beaver has increased to a conservative estimate of 700,000 individuals, and mostlikely, the overall population has more than one million individuals due to these efforts. Eurasian Beavers were valued for their fur, meat, and castoreum (exudates from castor sacs) for medicinal purposes. Composition of castoreum is influenced by diet and reportedly contains a large amount of salicylic acid, an active ingredient in aspirin. Castoreum has been used to treat headaches, pains, and digestive disorders. Numerous place names that refer to beavers across Europe attest to their long association with humans. Viable populations now exist throughout western and central Europe, and hunting seasons are allowed in many countries. Introduction efforts have brought the Eurasian Beaver back from the brink of extinction, and recent reintroduction efforts are underway in new areas such as Spain and the UK. Historical distributions include Portugal, Italy, and the South Balkan region including Turkey, but no populations currently exist there. A measure of the return of the Eurasian Beaver is the number of complaints of damage due to flooding caused by beaver dams that impound water and raise the water table. Loss of timber and flooding of agricultural land are occurring in areas where Eurasian Beavers had been absent from the landscape for hundreds of years. Impacts of increasing and spreading beaver populations on agriculture, other land uses, human structures, managed forests, roadways, road culverts, and railway beds, and how humans will learn to live with these impacts, are continuing concerns. Nevertheless, the successful return of the Eurasian Beaver andits ability to increase and enhance wetland function represent a conservation success story. Eight geographical subspecies of the Eurasian Beaver have been traditionally recognized based on geographic distribution and morphological differences. However, recent genetic analysis does not support subspecies status for any of the geographical groups in Eurasia. The Chinese/Mongolian form (historically considered the subspecies birulai) and the Tuva form (historically considered the subspecies tuvinicus) are the most vulnerable to local extinction given their small population sizes and distribution. There is still the possibility for human activity to negatively impact the Eurasian Beaver, especially because human use of water sources and wetlands might not be compatible with sustainable beaver populations. The issue of genetic purity of the Eurasian Beaver in various locations is also an ongoing conservation issue. Introduced populations of North American Beavers exist in Finland, Russian Karelia, Russian Far East (Kamchatka and Sakhalin Island). It is also possible that North American Beavers are present in Luxembourg, France, Germany, and Austria due to animals escaping from zoos or animal parks. A number of active projects are underway to use genetic methods to identify North American Beavers and remove them as competitors to the native Eurasian species. The similarity in form and behavior between the two beaver species creates concern that the invasive North American Beaver might be a competitor with the native Eurasian Beaver.

Bibliography. Biedrzycka et al. (2014), Busher & Dzieciolowski (1999), Busher & Hartman (2009), Coles (2006), Danilov et al. (2011a, 2011b), Dewas et al. (2012), Doboszynska & Zurowski (1983), Durka et al. (2005), Frosch et al. (2014), Gabrys & Wazna (2003), Gard (1961), Halley & Rosell (2002), Hartman (1994, 1996), Horn, Durka et al. (2011), Horn, Prost et al. (2014), Jenkins & Busher (1979), Kuehn et al. (2000), Lahti & Helminen (1974), Lavrov & Orlov (1973), Mors & Stefen (2010), Nolet & Rosell (1998), Parker et al. (2012), Richard (1967, 1973, 1980, 1983), Rosell & Pedersen (1999), Rosell & Schulte (2004), Rosell & Sun Lixing (1999), Rosell et al. (2005), Sharpe & Rosell (2003), Sjoberg & Ball (2011), Troszynski (1975), Wilsson (1968, 1971).

Figures

Distribution. N, C & E Europe, from Scandinavia and Russia to S France (Rhone Delta), extensive and small isolated populations in W & C Siberia, and in the Amur Basin, Russian Far East, and small relic populations in the Altai region of SW Mongolia and NWChina.