Beavers
Find out everything you need to know about the world’s second largest rodent!
What are beavers?
Beavers are the second largest rodent in the world. They have thick brown fur, scaly tails and webbedhind-feet. Adults can measure over a metre from head to tail.
Beavers are known for their big, strong teeth which they use to cut through tree trunks. Iron in their tooth enamel gives the teeth an orange colour and makes them super strong. The teeth stick out in front of their lips to allow beavers to chew underwater. Even strong teeth get worn down by gnawing through trees so their teeth never stop growing.
Why are beavers so important?
Britain is the 29th most nature-depleted country on earth and our natural systems are on the brink of collapse.
Beavers have the ability to breathe life back into our rivers and these effects are felt across all ecosystems in our country.
How do beavers do this?
Wetlands are known as carbon sinks and have been found to store up to 5 times more carbon than dry areas. By building dams on areas with small streams, channels and burns, beavers turn areas that were mostly dry into wetland which increases the level of carbon stored in the area.
Beaver dams slow the flow of water through a river catchment and increase the ability of the wider landscape to absorb and retain water. This reduces peak flow downstream, which is hugely beneficial to towns and villages at risk of flooding. This same principle also leads to improved drought mitigation.
Beavers are a keystone species. This means they have a disproportionally large impact on their natural environment.
Beaver basics
Beavers are excellent swimmers and can swim up to eight kilometres per hour (five miles per hour). They spend a lot of time underwater and can hold their breath for up to fifteen minutes. They also have an extra pair of eyelids which are transparent. These are closed underwater to act like goggles.
Many people believe that beavers eat fish. This is a common misconception. They are herbivorous which means they eat leaves, bark, twigs, roots and aquatic plants. Despite their eagerness to cut down trees they do not eat wood. Instead they eat the cellulose underneath the bark and use the wood to build dams and lodges.
Beavers are semi-aquatic which means they live partly on land and partly in water. Ideal habitat for beavers would be an area of fresh water surrounded by woodland.
Beavers have a good sense of hearing, smell and touch but their eyesight is poor and they are slow on land so they rarely go more than twenty metres away from water. They build dams and canals to create ideal living conditions and to provide water routes to and from food sources.
There are two species of beaver – the Eurasian beaver (Castor fiber) and the North American beaver (Castor canadensis).
Eurasian beavers are native to Europe, Scandinavia, Russia with isolated pockets as far east as Mongolia. They were reintroduced to much of Europe except Ireland (there is no evidence that beavers ever colonized Ireland) and remain absent from Greece.
North American beavers are native to and live throughout North America and Canada but introduced populations can also be found in southern America. North American beavers are also present in Finland and Russia. This is due to past introductions as part of the fur trade before the two beaver species were recognised.
Male and female beavers are monogamous meaning they usually stay with the same partner for life.
Baby beavers are called kits. Female beavers give birth to between 1 and 4 kits per year with most born in May/ June. Kits usually stay with their parents for up to 2 years before leaving the family unit to find a mate and set up a new family.
Beaver tails have many uses. They are used like rudders in the water to steer whilst swimming. They are also used as props for balance when they are sitting and to aid them whilst carrying large branches.
Beavers will also slap their tails on water to warn other beavers of potential danger.
People often believe beavers have no predators in Britain due the absence of the European wolf, European lynx and brown bear but young beavers, particularly kits, can still be predated on by red fox, domestic dogs, pine marten, birds of prey and even large pike!
There is also evidence that otters, American mink and badgers are opportunistic predators of kits.
Beavers are slow on land but more nimble in the water, so if any danger arises they need to be close enough to the water’s edge to get away quickly.
Dams are multi-functional, leaky structures. One of the primary reasons for constructing dams is that by slowing the flow and creating areas of deeper water, extremes in water levels are avoided. This keeps the pond level stable and lodge/burrow entrances submerged, protecting them from predators.
Dams are also constructed to open up new foraging opportunities that would’ve been too far from the water’s edge.
While they create areas of water which act as shelter for the beavers, dams themselves don’t act as shelters.
The majority of beaver dams aren’t associated with lodges, are often seasonal and have great ranges in longevity. They can range from inconspicuous forms made of mud to impressive structures made out of wood, mud and stones usually built on shallow rivers, streams and ditches.
Beavers may not always live in lodges but instead live in large burrows dug into the banks of rivers. These can extend for several meters and contain one or more chambers.
Burrows can have multiple functions, generally places of shelter but canalso be constructed to access forage resources.
The majority of all beaver shelters start off as a burrow/are aburrow/chamber complex – what you may see above the ground we calla lodge or burrow.
Lodges and chambered/natal burrows have more than one entrance, but not every burrow will have more than one entrance below the water.
Beavers build lodges out of woody debris, twigs and soil. Lodges can be found in the middle of a beaver built pond or at the side of a river.
Lodges are accessed via water-filled tunnels which keep the beavers safe from predators. Beavers eat, sleep, keep warm and raise their young in lodges. They also use them as food stores to keep them going during winter months.
Beavers consume a wide range of plants available in their territories including non-native plant species such as Elodea, Japanese knotweed and Himalayan balsam. Although their feeding may promote the establishment of non-native species (through disturbance, cutting and spreading of fragments) whether this significantly increases the distribution of such species is yet to be determined.
Like all native mammals, beavers can carry a range of pathogens and host-specific parasites. Long-term health monitoring of Scottish beavers has revealed they do not appear to be significant reservoirs of diseases and the risk of introducing significant disease to humans, domestic animals or wildlife from captive bred or wild beavers in Britain was low. Any translocated individuals are screened for a range of pathogens of concern before being released.
Current research creates a complex picture with estimates ranging from beaver wetlands being viewed as carbon sinks to carbon sources.
By transforming dry areas into wetland through damming, beavers increase the amount of carbon that can be stored but the area’s rewetting also results in methane being released into the atmosphere. Unmaintained beaver wetlands which return back into a dry state will release the carbon that was previously stored while it was a wetland.
Beavers can help us build landscapes that are more resilient to climate change though as their wetlands can reduce the risk of drought and flooding downstream as well as potentially helping us limit the spread of wildfire.
The impact beaver dams have on migrating fish is likely to be complex, site specific and change over time. In low flows, dams can form temporal barriers to fish movement, and in man-made canalised channels fish passage may be limited.
During high periods of flow beaver dams can be passable and in naturalised areas where the river is given sufficient buffer from intensive land use it can potentially cut around a dam creating side channels migrating fish can utilise.
Recent research in Scotland found that Brown trout benefited from the increased availability of suitable habitat and food source created by beaver damming activity.
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History
Beavers once roamed across our countryside, shaping the landscape and waterways
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Biology
Beavers are the second largest rodent in the world
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Impacts
Beavers are often called “ecosystem engineers”
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Donate today
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