Rediscovering the Eurasian Beaver

With an absence in Britain that exceeds our lifetimes, and a presence which has largely escaped our heritage, we need to reacquaint ourselves with our once-common neighbour, the Eurasian Beaver.

In this article, Cumbria Beaver Project Officer, Heather Devey, shares all you need to know to start your journey in rediscovering this intriguing, and vital, species.

Beavers: a short history

For around 400 years Eurasian Beavers (Castor fiber) have been absent from our British landscape, until recently. To us, 400 years might seem like a long time, and it’s true to say that a lot has happened in Britain in this time, but when it comes to wildlife and returning missing pieces to our ecosystems, we need to take a step back and contemplate things beyond our own timeframes.

The Beaver family first started evolving around 35 million years ago, according to the fossil record, with our very own Eurasian Beavers first making an appearance during the ‘Pleistocene’ epoch, around 2 million years ago.

To put that into perspective, modern humans are thought to have only arrived on the scene a mere 200,000 years ago, meaning we, and our ancestors, have lived in coexistence with these spectacular mammals for millennia.

Humans and beavers have co-evolved. We have shared the same waters, foraged from the same riparian land, and developed interconnected ancestral cultures for the past hundreds of thousands of years. Right up until a mere 400 years ago in Britain. Around this time, beavers were hunted to extinction for their fur (largely for hat making), meat and castoreum; a gland secretion which was – and in some countries still is in part -used in perfumes, foods and medicines.

With very few cultural references to Beavers in our fairytales and ancestral stories (compared to the likes of Wolves and Bears), and a near complete absence of it in our education system, very few of us know much about the basic ecology of the Eurasian Beaver.

So we need to spend a little time rediscovering this fascinating mammal, who we have so far welcomed back into Scotland1 and England2, with investigations underway for a Wales reintroduction by the Welsh Beaver Project.

A fascinating anatomy

What better way to begin your journey of discovery than a short, fact-filled 101 on the fascinating anatomy and ecology of beavers. Let’s begin.

Beavers are semi-aquatic rodents; the second largest rodent in the world in fact, just pipped to the post by Capybaras who claim the Worlds Biggest Rodent title.

Males and females are incredibly similar making them difficult to differentiate, particularly as they share an uncommon anatomical feature for placental mammals; a cloaca, which hides their genitals. Both genders have ‘castor sacs’, responsible for the aforementioned secretion, which are used for scent marking.

Beavers have webbed hind feet to aid in their semi-aquatic lifestyle, along with a broad ‘scaly’ paddle tail which not only acts as a rudder to facilitate underwater maneuvers, but assists in balancing when carrying ‘building materials’ short distances on hind legs. It also provides an effective, surprisingly loud, warning system when slapped on the water’s surface.

Their fur contains a staggering 10,000 hairs per square inch, with water-resistant guard hairs coating them; an essential asset for a mammal which spends most of it’s life in water in all seasons; on that note, Beavers do not hibernate.

Perhaps best known for their large teeth, Beaver incisors continuously grow, so all that gnawing comes in handy to keep them in check. The orange appearance of their teeth isn’t a sign of decay, it’s caused by iron in their tooth enamel, and yes, that does make them very strong. The outer layer of their teeth is hard enamel, whilst behind lies soft dentine, which wears away with gnawing action. So, incredibly, Beavers create their own chisel-like tools – perfect for the job of coppicing trees.

Talking of coppicing trees, Beavers ‘fell’ some trees to access the delicious, upper leafy branches, and to provide essential materials for dam and lodge building. Coppicing of large trees mainly takes place in winter, when ground vegetation is scarce. By coppicing trees, Beavers open up the canopy which enables an essential habitat, to develop; a shrubby understory. Shrub habitat is vital for a variety of different species; nesting birds in particular, providing shelter and food for much of our wildlife.

Beavers are entirely herbivorous, and feast on vegetarian banquets of grasses, aquatic plants, riverside vegetation, and, as mentioned, the inner bark of trees; with a particular fondness for willow, alder, aspen, birch and other deciduous species. Contrary to popular belief, and still portrayed in popular culture, Beavers do not eat fish! Not being the most agile creatures on land, Beavers prefer to forage within 20 meters of the waters edge, and their access runs between land and water are a tell-tale sign of their favoured feeding ground.

Ecosystem architects

There is still a lot we could explore about Beavers and their incredible ecology, biology and history, but let’s get to perhaps their most important attribute; wetland creation.

There are two terms used to describe Beavers:

  1. Ecosystem Engineers A species which creates its own habitat, and thereby modifies and maintains new ecosystems; altering the species richness of an area.
  2. Keystone Species An organism which has a considerable, overarching influence on the presence and survival of other species, more than its body mass would usually account for.

These terms are attributed to them due to their ability to create wetland habitats, and their influence in improving the health of aquatic ecosystems.

When a beaver, or pair of beavers, enter – say – a narrow tributary to a river, they may create a series of dams using sticks, stones and mud. This compounds the water, allowing pools3 to form behind each dam (often 2 meters in depth), which is important as Beavers are cumbersome on land, and have evolved to escape predators by submerging into water. Beavers do not tend to dam wide rivers; not only is this a difficult task, but most wide shallow rivers are too fast flowing for them to establish in, whereas slow flowing rivers in lowlands usually offer enough depth for them already.

The other habitat feature beavers actively create is a lodge; where they will rest and raise their kits (young) in. These are made with the same materials as dams in a dome like structure, and are usually situated at the side of the water, with several underwater entrances. If beavers establish a territory on a very slow flowing large river, they may create a burrow in the bank instead of / as well as a lodge.

The water captured through Beaver activity is where the magic begins. What was once a shallow ditch, transforms into a flourishing wetland habitat – brimming with new life. In the pools themselves, invertebrates such as dragonflies, mayflies and damselflies begin their lifecycles within the natural debris collected. First as sheltered eggs, then as larvae which must evade the new abundance of amphibians in the wetland, as well as fish such as salmon and trout4,the parr nurseries of which lurk in the shaded, slow flowing water.

Once the invertebrates emerge in their winged adult forms, they provide food for songbirds such as Spotted Flycatchers and Warblers which nest in shrubs, recently established in the new open tree canopy. Bats hunt from their abandoned woodpecker hole roosts, hidden within the standing deadwood habitat created by beavers. This tiny paragraph is a mere glimpse at the incredible biodiversity benefits beaver wetlands create; their presence results in an outstanding increase diversity and abundance of life.

A diversity and abundance of wildlife is supported by Beaver wetland creation (European Toad, Garden Tiger Moth, Water Vole: RSPB Images)

Nature’s solution to water management

Not only do Beavers benefit biodiversity, they offer a nature-based solution to improving the health and function of river catchment. Beaver wetlands and pools act as sponges, holding water back during flash flood events; with networks of dams reducing the speed of flow for catchments downstream. During drought events, pool water remains, providing an essential base flow, as well as a vital life-support system for wild animals and plants.

Dam network slowing and purifying water following a storm event in January 2020 (H. Devey, Bamff Estate)

In addition to these ‘leaky dams’ restricting the fast flow of water, they capture organic sediments, agricultural runoff including nitrates, and harmful chemicals such as pesticides, improving water quality downstream. Of course beavers can create localised impacts such as flooding and coppicing unsuitable trees, but the great news here is that there are tried and tested methods of preventing and mitigating impacts; such as installing flow devices and tree guards; which are all explained in detail in The Eurasian Beaver Handbook by Campbell-Palmer et al, 2016.

The ecosystem benefits of beaver habitats are so complex and intricate, they are quite simply irreplaceable. There is a well established, and increasingly growing, body of work on the impacts of beavers throughout Europe, and now in Britain, which highlight that their benefits can be enjoyed alongside human activity. To welcome the return of Beavers and their engineering to Britain, is to welcome an effective nature-based solution for a more resilient, healthy ecosystem, for wildlife and people.


1 In Scotland, the Knapdale Beaver Trial was the first official reintroduction project, with reintroductions on the Bamff Estate taking place prior. Beavers are now free-living in parts of Scotland; particularly on the Tay catchments, with Scottish Wild Beaver Group providing education, advice and support to communities.

2 In England, the River Otter Beaver Trial is the first licensed Beaver reintroduction. Enclosed trials have been increasing in popularity and importance in the past few years, including (but not limited to) the Cornwall Beaver Project and Cropton Forest Beaver Trial.

3 The River Otter Beaver Trial (ROBT) identified that 13 pools were created by beavers in one year, each storing around 1000m3.

4 ROBT found that fish abundance in beaver pools was 37% higher than in control sites.

Heather Devey

Heather is Beaver Project Officer with the Cumbria Beaver Group, of which RSPB is a key partner alongside Cumbria Wildlife Trust, Eden Rivers Trust and Lowther Estate, in addition to a number of advisory consultants. A license for the first enclosed, trial reintroduction of Beavers in Cumbria was approved for the Lowther Estate at the beginning of 2020. The Cumbria Beaver Group can be followed on Twitter or contacted at [email protected]. Heather is also Visitor Development Officer at RSPB Haweswater.

The RSPB supports the return of beavers to their historic range in Britain through well-planned and supported reintroductions, particularly in areas which will gain ecologically from their presence.

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