Eurasian Beaver

Appearance

The fur colour of Eurasian beavers varies geographically. Light, chestnut-rust is the dominant colour in Belarus. In Russia, the beavers of the Sozh River basin are predominantly blackish brown, while beavers in the Voronezh Reserve are equally distributed between brown and blackish-brown.

Eurasian beavers on average weigh 18 kg, the largest specimen on record having weighed 31.7 kg.

Naming

Historically eight subspecies of Castor fiber were described, one for each of the eight 19th–20th century refugia where the species never became extinct. The basis of the differentiation was morphological, largely based on very small differences in cranial morphology, but has been recently refuted based on genetic studies. In 2005, Durka ''et al.'' showed that only two evolutionarily significant units exist based on mitochondrial DNA studies, a western phylogroup and an eastern phylogroup . In addition, Ducroz ''et al.'' found that even in the more genetically diverse eastern phylogroup, the degree of genetic divergence was below thresholds considered sufficient for subspecies differentiation.

Habitat

Beaver are a keystone species helping support the ecosystem of which they are a part. They create wetlands which increase biodiversity and provide habitat for many rare species such as water voles, otters and water shrews. They coppice waterside trees and shrubs so that they re-grow as dense shrubs which provide cover for birds and other animals. Beaver dams trap sediment and improve water quality; recharge groundwater tables and increase cover and forage for trout and salmon. A recent study in Poland, found that beavers increased abundance and diversity of bats apparently because they create gaps in forest cover making it easier for bats to navigate in.

Reproduction

Eurasian beaver have one litter per year, coming into estrus for only 12 to 24 hours, between late December and May but peaking in January. Unlike most other rodents, beaver pairs are monogamous, staying together for multiple breeding seasons. Gestation averages 107 days and they average three kits per litter with a range of two to six kits. Most beaver do not reproduce until they are three years of age, but about 20% of two year old females reproduce.