European beaver ecology

What is a Beaver?

Beavers are large, bulky mammals with distinctive incisor teeth and a paddle tail. They are the second largest rodent in the world weighing in between 11 and 26kg and growing up to 4 foot long! There are two species of Beaver both widely distributed in the northern hemisphere, the North American beaver, Castor canadensis, and the European beaver, Castor fiber, which ranges across from Europe to China and Mongolia.

They are very well adapted to their amphibious lifestyle, they have their eyes, ears and nostril high up on their head so when swimming they can still use all their senses without exposing too much of their body. They are also in possession of a big flat tail which is used to store fat, steer themselves through the water and slap to ward of predators. They have a streamlined torpedo-shaped body for swimming underwater, generously webbed hind feet and a double-layered fur with outer guard hairs for waterproofing and a dense underfur for warmth. It’s really important that the beavers groom regularly to keep their fur waterproof and insulating. To do this they use their second toe on their hind foot which has a double claw which can be used as a primitive comb and sometimes they can be seen grooming each other.

Beavers are highly social animals, living in family groups, in and around freshwater. They are a very important part of the aquatic environment and are known as “keystone species” because of their benefits to other species and the habitats they create.

Beavers love water they feel safe in the aquatic environment. Any sign of danger and they can disappear under water. They can swim at an amazing 2.1 metres per second and can stay underwater for 15 minutes! Their main predators are land based mammals such as the Brown Bear (Ursus arctos), Wolf (Canis lupus), Lynx (Lynx lynx), Wolverine (Gulo gulo) and the Fox (Vulpes vulpes). In Scotland, most of these are now extinct, but retreating to the water for safety is instinctive to escape these predators. The young can also be taken by White-tailed eagles, otters, and predatory fish such as pike.

Food

Beavers only eat plant material (they don’t eat fish). Their huge incisors (two front teeth) and molars are used to chew vegetable matter. Beavers have a gap between their incisors and their premolars called a diastema. This enables them to suck in their cheeks to close up their mouths so they can feed underwater.

All in all they have been recorded to eat 80 species of tree and nearly 150 species of herbaceous and aquatic plants. Beavers won’t eat conifers but the leaves, bark and cambium layer of deciduous trees especially aspen, willow and birch is very tasty. Another favourite is the water lily, beavers will eat the leaves, the flowers and the rhizomes (root stores). As a result their diet is highly seasonal, in spring and summer the diet is dominated by terrestrial and aquatic herbaceous plants while in autumn and winter food is mainly bark from trees.

Plant material is difficult to digest so they have micro-organisms living in their gut which have enzymes to break down the tough plant material. Beavers eat vast quantities in order to obtain sufficient energy.

Beavers are famous for felling trees. The reason they like to fell trees is not only for building material but also so they can access more food in the form of bark, cambian and leaves that would normally be out of reach. The record diameter for a beaver felled tree is 106cm! Their large front teeth are ideal for chipping away at the trunk of a birch, willow or aspen tree, but beavers don’t actually eat the wood of trees. They can bite through wood to fell trees or to make large sticks more manageable. They will always spit the woodchips back out leaving a litter of chips around the felled tree.

They like to fell trees near the waters edge and also towards the water so they can float them easily to their lodge or dam.

Importantly the felled tree is not dead. Often willow branches will re-root even after they have been dismembered. Also, the favoured trees all coppice well, so the stump left behind will re-grow vigorously the following spring. With a root biomass large enough to support a tree these coppiced trees soon regenerate and this can extend the life of the tree and also create new young shoots for other species to feed on.

Dams

Beavers sometimes build dams to raise the water level of a particular area. They are hard-wired to stay in water for safety from predators, so if they want to access more trees they sometimes extended their loch or create new lochs. Beavers are stimulated to build dams where they can hear running water and begin damming where the sound of water is loudest. They use sticks to construct the dam and mud is plastered over it to make it watertight. On large rivers or tributaries dams cannot be built as the current is too strong. Eurasian beavers do not normally build large dams unlike their American relatives which have been recorded building dams 650m in length!

Lodgings

Beavers live in lodges which are constructed in a similar way to dams (sticks and mud). They can also dig into the bank of a river or loch and create a series of tunnels and chambers. The entrance is always under water, protected by sticks, again for protection from predators. If the entrance is not underwater they will build a dam to raise the water level. Just beyond the entrance is a feeding chamber with tunnels leading to the sleeping chambers. Usually they take about 20 days to make. Imagine building your house that quickly!

Habits

Beavers are nocturnal. Their whiskers are important for feeling their way around in the dark as is their sense of smell and hearing.

Beavers are “Keystone species”. This means they are very important and even essential to the environment. There are endless reasons why beavers are so important to ecosystems but the bottom line is that they promote diversity encouraging species of plants to invertebrates to mammals to thrive. They create wetland habitats, standing deadwood, aquatic deadwood and filter the water. The ponds they establish create new opportunities for all sorts of aquatic plants, which in turn are food for aquatic and terrestrial invertebrates, in some studies the number of dragonfly species has trebled. This attracts fish and amphibians, which in turn will attract otters, ospreys, white-tailed eagles, and so the list goes on.

Beavers also open up forest canopies creating enough natural disturbance to promote regeneration and allow understorey plants to flourish.

The History of Beavers in Britain

Beavers were widespread on mainland Britain but were hunted to extinction about 450 years ago. Castoreum (an oil secretion from the anal gland) was thought to have medicinal purposes, their meat was considered good to eat and their fur made excellent hats for cold weather because of its insulating and waterproof properties. There have been over 20 successful reintroductions in Europe including in Sweden, Norway and Poland. Scotland has ideal beaver habitat……………

Reintroducing Beavers to Scotland

On Sunday 25^th May 2008 the Scottish Government accepted the proposed trial re-introduction of beavers to Knapdale on the West coast of Scotland! This will be the first formal re-introduced of a native mammal to the UK! There will be up to four families of beaver released in spring 2009 which will be closely monitored before a possible further re-introduction takes place. This is great news and a step in the right direction!

 The beaver’s role as a keystone species has been evident for a long time and its reintroduction to Scotland would have ecological benefits. Their dams sustain water flow and prevent flooding. Their engineering also enables slow release of water during dry periods. Diversity of the riparian zone (the area around the river) increases with the presence of beavers. They raise the level of the water table which is good for crops.

 Overall the Scottish people are behind the reintroduction, provided that there are suitable management controls in place, but there are some groups, for example fishermen and foresters, who are against the reintroduction of the beaver. Several groups in support of the beaver have been campaigning for the reintroduction and it is predicted Scotland as it is can support over 1,000 beavers all over Scotland.

The Aigas Beavers

A male and female beaver were released into the Aigas loch in April 2006. Since then we’ve seen them build their own lodge, feed on willow, birch and lilies, fell numerous trees and have a total of three kits over two years! It’s been very interesting to follow their behaviour in an accessible wild-like situation. We do not usually feed the beavers, we leave them to their own devices within their large enclosure. We’ve had lots of people come and visit the beavers including the BBC!

 Click here to see the latest action in the Aigas Beaver Diary

 Links

 Scottish Beaver Network - http://www.scotsbeavers.org/index.htm

 SWT - http://www.swt.org.uk/about_us/beaverCampaign.asp

 Trees for life - http://www.treesforlife.org.uk/tfl.eb.html

 BBC News - http://news.bbc.co.uk/1/hi/scotland/7158210.stm

BBC Nature (Video) - http://www.bbc.co.uk/earth/nature/uk/records/tagged/european%20beaver

Beavers: Wildlife and Wetlands (American) - http://www.beaversww.org/

 SNH Information, Publications and Species Action Framework - http://www.snh.org.uk/speciesactionframework/saf-europeanbeaver.asp

 Royal Zoological Society of Scotland - http://www.edinburghzoo.org.uk/PageAccess.aspx?id=211

 Text researched and presented by Ian Sargent. All photos are of Aigas Beavers.