Beaver facts

Did you know that beavers are Europe’s largest native rodent; that they can remain under water for up to 15 minutes at a time and are highly skilled water engineers? More fascinating facts can be found below…

Which species?

There are two species of beaver: the North American beaver ( Castor canadensis ) and the Eurasian beaver ( Castor fiber ). It is the Eurasian beaver that is native to Britain.

How big are Eurasian beavers?

Beavers can grow to the size of a tubby spaniel - they usually weigh between 16 and 30kg, measuring 60–90cm in body length, with tail lengths of 20-35cm.

It is hard to tell the sex of a beaver from its appearance. Unusually for mammals, female beavers are the same size or slightly larger than males of the same age.

Beavers are uniquely adapted for a semi-aquatic lifestyle, with a sleek waterproof coat, large flattened muscular tail and webbed hind feet to provide propulsion underwater.

How long do they live for?

Beavers can live up to 25 years in captivity, but would not live as long in the wild – possibly 15 years.

What is castoreum?

Castoreum is an oily substance secreted from a scent gland at the base of the tail.  Beavers use this substance in combination with urine to scent mark their territory.  Castoreum is also rich in salicylic acid, a basic ingredient of modern aspirin drugs, and was widely used in Medieval times as a treatment for headaches.

What do beavers eat?

Beavers are herbivorous and do not eat fish. They feed on aquatic plants, grasses and shrubs during the summer months and resort to more woody plants in winter. They will often cache food underwater near the lodge so that they can access it if the water freezes over.

In woodland environments, beavers help to diversify the woodland structure by coppicing larger trees, and stimulating regrowth. This helps to create a diverse age range of trees which greatly benefits woodland biodiversity.

Do beavers build dams?

Beavers are well known for their construction skills and are considered ‘keystone’ species because of the unusually large effect that they have on the environment in which they live, which, in turn, creates the right conditions for many other species to live.

This rodent feels at home in slow-flowing waters – beavers like to move around in water which is at least one metre deep so that they can search for leafy food safely, under cover. This is why they build ponds by making sophisticated dams along streams, and why they dig canals – to make foraging routes to seek out tasty young willow growth and tree bark.

When beavers do dam, this modification can have a positive effect for biodiversity. Their ponds benefit many species including otters, water shrews, water voles, birds, invertebrates (especially dragonflies) and breeding fish. Dams can also hold water in periods of drought, can regulate flooding and improve water quality by holding silt behind dams and catching acidic and agricultural run-off.

When do beavers start breeding and do they hibernate?

Beavers are highly territorial and live in family groups, with a family group occupying a few kilometres of river or stream, or wetland or freshwater lochs. Beavers are crepuscular, rather than nocturnal, meaning they are most active at dawn and dusk throughout the year and do not hibernate.

Beavers are thought to be monogamous, which means they mate for life or until their partner dies. A breeding pair can produce 2-4 kits per year. Mating takes place between January and February, with kits born within the lodge from April to June (gestation of around 105 days). Other family members may bring vegetation to the lodge for kits to feed on during this time. Kits are usually weaned after 2-3 weeks and emerge from the lodge to feed with their parents during June or July.

Offspring will remain with their parents until they are around two years old. Around this period they become sexually mature and leave to find territories and partners of their own.

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