Castor fiber

Order: Rodentia                  

Beaver and kit – photo: Carrie-anne Goodchild

Description: Large bodied with a blunt snout. Eyes, ears and nose sit high up on their head enabling them to keep a low profile in the water. Feet are webbed and they have a large flat, hairless tail.

Size: About 80-100cm; tail about 30m

Weight: Average 20-30kg. Females are on average 1-1.5kg heavier.

Lifespan: Approximately12-14 years, mortality is high in the first 2 years of life.

Breeding: Breeding occurs Dec-April with kits being born around May/June. Beavers live in family groups compromising of a pair of breeding adults who typically mate for life. The female will give birth once a year with an average litter size of 1-4.  Kits are born fully furred and they learn to swim within hours. The young stay with the family for around 2 years or until they are ready to establish their own territory. Beavers are highly territorial and will use their scent glands and scent mounds to mark their territory.

Habitat: Fresh water streams, rivers and lakes. Beavers favour slow moving water with close access to deciduous woodland.

Diet: Beavers are entirely herbivorous feeding on aquatic plants, grasses and bark. In the summer months a large part of their diet consists of aquatic vegetation. In the winter months beavers will transport wood material to lodges or burrows so they can still feed if the water freezes.

Although they can fell trees with diameters wider than 1m they prefer smaller saplings. Birch, Willow, Aspen and Alder are particularly favoured.

General Ecology: Beavers are known as a keystone species. They are able to alter their environment and create new ponds/wetland areas which benefits many other species and improves the water quality downstream.

Burrows are dug into river banks and if suitable areas cannot be found they will build one from felled trees and mud. Beavers are of course famous for their dam building, however European beaver dams are not as spectacular as their American cousins (Castor Canadensis). In general dams are only built if the natural landscape is not suitable for the beaver’s needs, if it is not they will build dams to retain and manage water levels. As a result, this helps to reduce flooding downstream during heavy rainfall.

Beavers are largely nocturnal but can sometimes be seen at dawn and dusk, they do not hibernate so can be seen all year round.

Beaver 2km2 to 2018

Distribution and main sites: Beavers were once widespread throughout most of Europe but hunting for their fur, meat and musk scented secretions known as castoreum, decimated their numbers and they became extinct in the UK in the 16th century.

Throughout Europe translocation and reintroduction programs have helped to re-establish beaver numbers back into their former ranges. In Britain beavers were unofficially released in Knapdale, Argyll and the river Otter, Devon. Official reintroductions programs were carried out in Scotland in 2009 and in 2016 the Scottish announced they would be allowed to remain. The Devon beaver trial started in 2015 and will run for 5 years and in recent year’s number of reintroductions programs have been proposed in several locations throughout England and Wales including Shropshire from where the animals are currently absent.

Threats: Road traffic collisions, habitat loss, river pollutions and human persecution.

Action: The Shropshire Wildlife Trust is currently in the early stages of a possible Beaver reintroduction in Shropshire. The Welsh Beaver Project is currently seeking approval for a reintroduction in Wales.

Main recording methods: field signs including tree felling (distinct teeth marks left on tree and wood chippings around the base), dams, lodges and direct sightings.

Did you know? Beavers have chisel like orange incisors. The orange colouring is due to iron replacing calcium in the enamel.

In medieval times the glandular oil (castoreum) was believed to have medicinal purposes and was used as a headache cure.

Field Signs

Beaver dam – photo: Malcolm Monie
Tree felling – photo: Malcolm Monie


Round pellets. Beavers frequently excrete whilst in the water where it quickly breaks down so sightings of droppings on land are rare.

Text: Carrie-anne Goodchild

© Shropshire Mammal Group 2020