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Eurasian beaver

Scientific name: Castor fiber

"They were standing on the edge of a steep, narrow valley at the bottom of which ran—at least it would have been running if it hadn't been frozen—a fairly large river. Just below them a dam had been built across this river; and when they saw it everyone suddenly remembered that of course beavers are always making dams and felt quite sure that Mr. Beaver had made this one.”

- C. S. Lewis – the Lion, the Witch, and the Wardrobe

Hunted to extinction in the UK by the end of the 18th century, the first official Eurasian beaver reintroduction into an enclosure took place on an enclosed wetland site in Kent in 2003. As ecosystem engineers, these large rodents modify the environment around them, most famously by building their distinctive dams.

Taxonomy chart

Animalia - Chordata - Mammalia - Rodentia - Castoridae - Castor - C. fiber

Conservation status: UK Red List

GB: Endangered

England: Critical

Scotland: Endangered

Wales: N/A

Global: Least Concern

Summary

Diet: Herbivorous. In the summer, beavers will eat vegetation such as rhizomes, pondweed, ferns and grasses, switching to wood and tree bark in the winter months.

Habitat: Riparian, usually associated with broad-leaved woodland.

Size: Between 74-90cm in length, excluding the broad, flat tail which measures between 28.5-35cm long. Weight is variable, typically anywhere between 12.5-38kg.

Lifecycle: Average lifespan is 8 years, but they can live up to 25. Young beavers are mature from the age of 2 and usually produce their first litter at 3, breeding between December and April and giving birth to 1-7 young in the summer, known as kits.

Conservation concerns: Beavers can alter and create wetland habitat and thus impact farmland; they hold potential for human-wildlife conflict if they colonise and cause new wetland areas that encroach on productive farmland, due to the current approach to agricultural land management often leaving minimal buffer between rivers/streams and fields. Beavers are a protected species so can't be culled without licence.

Terminology

Ecosystem engineer: An animal that actively modifies its environment, changing or creating habitat and affecting the resources available to other species.
Riparian: Wetland habitat, next to rivers or streams.

Castoreum: A secretion produced by mature beavers, used to mark territory.

Geography

Currently, wild beaver populations are known to be present on the rivers Avon, Frome and Otter in south-west England, and in Knapdale and the river Tay from Scotland. Small populations can be found in large, controlled outdoor enclosures across the UK.

Beavers are found in riparian habitats, close to freshwater and surrounded by wetland plants and woodland. They are often found in deep, slow-moving rivers or lakes, but in areas where the water is too fast or shallow, they will build their characteristic dams to slow the flow. Typically, they dig burrows into the riverbank for shelter, but where the bank isn’t suitable for digging, they will build lodges from wood, twigs and soil. These may be constructed on the riverbank, or in the middle of a pond created by damming the stream. These lodges offer protection from predators as they are surrounded by water and accessed from underwater.

Biology

The Eurasian beaver is the largest rodent in Britain. Its most distinctive feature is the flat, scaly, paddle-shaped tail, measuring approximately 28.5-35cm long. The body is between 74 and 90cm in length, and weight can vary from 12.5kg up to 38kg.

The head is blunt, with small ears and small, dark eyes protected underwater by a set of clear eyelids known as a nictating membrane. Their teeth are bright orange, due to their enamel being reinforced with iron, and their incisors are sharp and very fast-growing to compensate for wear and tear, adapted for gnawing at wood. Like all rodents, these teeth grow continuously throughout their life, and are filed down and sharpened by daily use. The body is stocky and short-legged, covered in dense, mid-brown fur that traps air when submerged in water, providing extra warmth. Although slow on land, beavers spend a lot of time in the water and are excellent swimmers, able to hold their breath for up to 15 minutes. As they can’t see well, they tend to rely on their other, keener senses, and can detect objects as well as the strength of currents underwater using their whiskers. The tail is broad, flat and hairless, functioning as both a rudder for swimming and as a warning signal; when threatened, they can slap it on the water’s surface to create a loud alarm signal.

They live in small family groups, usually consisting of a monogamous breeding pair and the young of that year, sometimes accompanied by the previous year’s young. Group sizes increase with population density and territory size is variable, dependent on density, habitat quality and season. An average beaver territory is 3km, but they can be as small as 0.5km or as large as 12.8km. Breeding takes place between December and April, and young are born after a gestation of just over 100 days, usually in May or June. Litter sizes can be between 1 and 6 kits, but 3 is average, with no more than one litter produced per year. Kits leave the nest at 1-2 months old and are fully weaned by the end of their first summer, but may not disperse from their family group until they are 2 years old. At this point they are sexually mature, but rarely breed successfully until their third year. Their average lifespan is 8 years, but they can live for as long as 25 years.

Ecology

Beavers are herbivores, feeding on bark, shoots, leaves and wood from both riparian and aquatic vegetation in the summer. In the winter, their diet is primarily composed of wood, and they will create underwater caches to ensure a ready food supply. When available, their winter diet consists predominantly of aspen, willow, poplar and alder. Beavers will typically forage close to riverbanks, rarely more than 20m from water.

As ecosystem engineers, beavers directly modify the environment they live in. By felling trees, they coppice woodland, allowing understorey plants to grow, enabling insectivorous birds and bats to feed, and increasing the amount of light reaching the water, which is shown to benefit amphibian breeding and freshwater invertebrate populations. They also create important deadwood habitat for invertebrates and fungi. Their dams prevent eroded soil being washed to sea, and improve water quality downstream by blocking sediment and filtering water. Beavers only dam rivers where the water is too shallow or fast-flowing, but they will also burrow into riverbanks or build lodges for shelter. Their dams can cause localised flooding issues, particularly where people are farming or using land close to a river.

Conservation

Outside of the UK, the Eurasian beaver has a wide distributed and is listed as Least Concern by the IUCN. They have experienced the same historic declines from over-hunting in Europe as in the UK, to the point of local extinction in many countries, but protection and reintroduction efforts across the continent has restored some of these lost populations.

In 2022, the Eurasian beaver received native species status across the UK, protecting them and their structures from killing, disturbance, removal or sale. Where management is required for conflict with humans, a trapping license is required from Natural England or NatureScot. Wild releases have been allowed under licence in Scotland since 2019 when legislation was approved to designate Eurasian beavers as a European Protected Species in Scotland. Prior to this, an assessment of the 2009 trial release in Knapdale in 2016 resulted in the government determining that the official Knapdale trial population and the unofficial Tayside population could remain in the landscape. In England, it was in February 2025 that the legislation was passed to allow wild releases under licence.

Socio-economic concerns remain the biggest threat to beaver conservation, such as negative attitudes and misunderstandings from farmers and other stakeholders. Beavers can alter and create wetland habitat and thus impact farmland; they hold potential for human-wildlife conflict if they colonise and cause new wetland areas that encroach on productive farmland, due to the current approach to agricultural land management often leaving minimal buffer between rivers/streams and fields.

History

The earliest Castor fossils are approximately 8 million years old, but the Eurasian beaver likely evolved later in the early Pleistocene, around 3 million years ago. During the late Pleistocene ice age, beavers seem to have disappeared from much of Europe and Asia, but populations quickly expanded to repopulate their original range as the climate began to warm again.

Beavers have been heavily persecuted through the UK and Europe, hunted for their meat, fur, and the castoreum they produce, which is very rarely still used today in perfumes and food. There is a belief dating back to ancient Egypt that male beavers would chew off their testicles, potentially because these organs are not externally visible. This myth continued in Medieval Europe, where beavers in art are usually depicted as running from hunters, and sometimes shown giving their testicles to the hunters. If a beaver was hunted for a second time, it was thought to roll over to show the hunter it had nothing left to offer. While there is no truth to either behaviour, it may indicate that the beavers at the time were primarily hunted for castoreum; though castoreum is not, as was believed in the past, produced by the testicles.

Beaver meat and fur was also historically popular. Christians were able to eat beaver meat on days when meat was traditionally disallowed; as they lived in water, beavers were instead classified as fish by the church. Although some populations persisted on mainland Europe, this hunting began to take its toll on beaver numbers, and the last sighting of a British beaver was recorded in the Loch Ness in the 1500s. Small, isolated populations may have lasted longer, as they are mentioned in a 14th century Welsh poem, and purchases of beaver heads were recorded in the early 1700s in Yorkshire. Following this, there is no trace of wild British beavers in the historic record until 2002, when the first official reintroduction to a fenced wetland site took place.

Since then, several fenced enclosure trials have taken place across the UK, and two licensed free-living populations can currently be found on the River Otter and in Knapdale, though there are many more ‘unlicensed’ free-living beavers across the UK. The Scottish government gave a license for a beaver reintroduction trial in 2008 to Knapdale Forest, yet the River Otter beavers in England were illegally reintroduced but allowed to stay under monitoring. In 2019, beavers were granted protected species status in Scotland, and in 2022 the UK government officially recognised them as a native species.

Identifying and surveying

Feeding signs: Beaver feeding signs are very distinctive. Gnawed wood will have large incisor marks, and larger trees may be felled completely, leaving clearly gnawed stumps in an hourglass shape.

Scat: Not easily found as usually done in the water and consists of pellets of loose wood pulp.

Lodges and dams: Beaver lodges are large piles of sticks and mud. Where riverbanks are high, beavers may burrow underwater, and these burrows become visible when water levels are low. Dams can look similar to lodges, but will be built perpendicular to moving water, and may be made of branches, vegetation, mud and stones.

Survey period: Beavers are active year-round, but most visible at dawn and dusk. Surveys usually look for signs of beaver activity, which may be more visible in winter when vegetation has died back.

Frequently asked questions

Beavers are not aggressive animals and prefer to avoid people. When threatened, they will typically flee into the water.
Daytime beaver sightings are possible, but rare. Beavers are for the most part crepuscular and nocturnal, active from late evening to early morning.
Beavers have large, distinctive orange incisors. Historically, it has been believed that the colour comes from their iron-rich enamel, which strengthens the teeth and protects them from damage. Recent research suggests the source of the orange colour is a thin layer over the tooth, rather than the iron in the enamel, but the function of this layer is unknown.
Beaver kits may be predated by foxes and birds of prey. Historically, adults may also have fallen prey to wolves and lynx.
No. Beavers eating fish is a common myth, with C. S. Lewis depicting the friendly Mr and Mrs Beaver as fish-eaters in the Lion, the Witch and the Wardrobe. In reality, they are strictly herbivorous, feeding on vegetation and wood.

Confusion species

Water vole (Arvicola amphibius)

The beaver and water vole are superficially similar, but the beaver is significantly larger. Water voles can reach up to 22cm in length excluding tail, whilst beavers may reach up to 90cm in length excluding tail. The water vole’s tail is thin and furred, very unlike the flat, hairless, paddle-shaped tail of the beaver.

Otter (Lutra lutra)

It may be possible to confuse beavers and otters in the water. Beavers are larger than otters and have a stockier build, with short legs and a blunt face, whereas otters are more slender and have a pointed, dog-like head shape. Beaver tails are distinctly flat and hairless, while otter tails are long and furred.