European beaver (Castor fiber)

The European beaver was an important part of the native fauna of the Caledonian Forest. Hunted to extinction by the 16th century, it is now poised to become the first of our extirpated mammals to be reintroduced.

 

Global Distribution

The European beaver was originally distributed throughout most of Europe and northern Asia, from Scotland to eastern Siberia. Within this range, beavers occurred along wooded streams and rivers, and in small ponds and lakes surrounded by trees. However, by the end of the 19th century beaver populations in Europe had been reduced to a few isolated sites in the Elbe River basin in Germany, the Rhône River basin in France, and southern Norway. Other small populations survived in Belarus, Russia and Mongolia. The main cause of this dramatic reduction in beaver numbers was hunting for their pelts, meat and castoreum (a secretion from their scent glands), although habitat loss was also a contributory factor.

Since the 1920s, beaver reintroductions have taken place in thirteen European countries, and by the early 1990s beaver numbers in Europe were estimated to have recovered to about 250,000. However, the International Union for the Conservation of Nature (IUCN) still classifies the beaver as `Vulnerable', meaning that it could become in danger of extinction in the future. (Note: the North American beaver (Castor canadensis)  is a different species, and has always been confined to Canada and the USA.)

Distribution in Scotland

Based on palaeontological and archaeological remains and historical evidence, scientists have concluded that the beaver was widely distributed throughout mainland Scotland, with bones having been discovered from Dumfriesshire in the south to Caithness and Sutherland in the north, as well as in Perthshire and Moray.

The exact date of the beaver's disappearance from Scotland is unknown, but it was certainly still present in the 12th century, when excise duty was collected on the export of its pelt. Written records indicate that it may have survived in small numbers at a few locations until the 16th century.

The beaver is the largest rodent native to Europe, with adults weighing 18-20 kg., and exceptionally, up to 29 kg. Head and body length is between 70-100 cm., while the tail is from 30-40 cm. long. The beaver is mainly nocturnal and is highly adapted to its semi-aquatic lifestyle, with sleek waterproof fur, a distinctive, hairless, flattened tail and webbed hind feet, which it uses for propulsion in the water. The beaver also uses its tail to slap the water surface when it is alarmed, before diving underwater and swimming away; it can remain submerged for up to fifteen minutes. The long claws on its front feet are adapted for digging, and the beaver is highly dexterous, being able to hold small objects between its toes while feeding.

Beavers generally live for 7-8 years, but have been known to live for up to 25 years. With most of their predators, such as the wolf (Canis lupus), brown bear (Ursus arctos), lynx (Lynx lynx) and wolverine (Gulo gulo), now very rare or extirpated from their former range, most beaver mortalities are caused by humans, through poaching, road accidents and entanglement in nets.

Beavers live in small family groups, usually consisting of 3-5 individuals and comprising an adult pair, kits, yearlings and one or more sub-adults. Females normally reach reproductive age at three years, and an adult pair produce one litter per year, consisting of 2-3 kits. A family group will have a territory which averages 3.6 km. of river bank, but can be from 0.5-13 km., depending on the availability of food. Territories are scent marked with castoreum, a secretion from the anal gland beneath the tail, which has long been known to have medicinal properties. (Castoreum contains salicylic acid, the main active ingredient in aspirin, and the hunting pressure for castoreum was one of the main causes for the beaver's historical decline in numbers.)

The European beaver prefers burrows in river banks as a nesting place, but it will build lodges of piled logs where burrowing is not possible. It builds fewer dams than the North American beaver, and it does so generally in shallow streams to maintain water levels above the entrance to its burrow. Dams are built of tree trunks, branches and mud, and are about one metre in height and rarely longer than fifteen metres. They are usually breached by flood waters each year, and do not normally pose any obstacle to the movements of fish such as brown trout and salmon .

The beaver is entirely herbivorous, and in the late spring and summer eats mainly aquatic plants, grasses, ferns and shrubs. At other times of the year, woody species form the major part of its diet, with aspen (Populus tremula), birch (Betula spp.), oak (Quercus spp.) and rowan (Sorbus aucuparia) being particularly favoured, although it will also eat willow (Salix spp.), alder (Alnus glutinosa) and ash (Fraxinus excelsior). Conifers are rarely touched. Feeding generally takes place within ten metres of the water's edge, and the beaver will rarely travel more than 100 metres from water. It prefers trees with a diameter of less than ten cm., but it is capable of felling trees up to one metre in diameter. In areas with harsh winters, the beaver will transport woody material to its burrow or lodge, storing it there so it can feed when the water is frozen. In common with other rodents, the beaver's incisors grow constantly during its life, and it needs to use these teeth regularly to prevent them from becoming too long. For this reason the beaver will sometimes gnaw trees without actually felling and using them.

Beavers are notable amongst mammals for their ability to alter their surroundings to make them more suitable as their habitat, mainly through the construction of dams, canals etc. These activities determine many of the relationships which beavers have with the flora and fauna where they live.

The felling of trees obviously has an effect on the riverside forest, but this rarely results in deforestation of the riparian zone. Their effect on many of the deciduous trees they fell is akin to a natural coppicing process - species such as oak, rowan and willow will send up new shoots from the stump of a felled tree, whilst aspen will also regrow, though its reproduction is by root suckers, or ramets. The presence of beavers therefore tends to encourage the production of young shoots or trees in many instances. Although flooding caused by dams can result in trees being drowned, it has also been postulated that beavers historically helped the spread of alder in Britain, by creating suitable habitat for these water-loving trees to grow in.

The ponds created by beaver dams favour the growth of aquatic vegetation and also result in population increases of invertebrate species. This in turn provides an enhanced food source for fish, amphibians and birds, which also benefits predators higher up the food chain such as otters (Lutra lutra) and grey herons (Ardea cinerea), which eat the fish. Otters are known to use beaver burrows and lodges, as do water voles (Arvicola terrestris), while several species of birds, including mallard (Anas platyrhynchos), teal (Anas crecca) and goldeneye (Bucephala clangula) nest on beaver ponds.

In North America, the beaver is considered a keystone species in river and pond ecosystems, and it is likely that the beaver would fulfil a similar vital ecological role here. After an absence of about 500 years, the proposed return of the European beaver to Scotland will mark a major and significant step forward for the restoration of our degraded and fragmented ecosystems .

Alan Watson Featherstone

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