Castor fiber
European Beavers are the largest rodents in Europe. They have streamlined bodies and short legs. They normally weigh between 13 and 21 kg, but females are larger and may weigh up to 35 kg; they are 70–90 cm long, with a tail measuring 25–40 cm long and flat like the blade of an oar; the skin on the tail is scaly and furless.
The beaver’s fur is a shiny greyish brown, with strong outer coat over a thicker, softer undercoat. Beavers live near lakes or moving water. They swim around quietly, only the head and a part of the upper back visible. When beavers dive, they may remain under water for 2–3 minutes, but they can also, if threatened, hold their breath for up to 15 minutes.
A dam ensures the water level stays high above the lodge. LG.
Beavers feed exclusively on plants. In summer they feed on succulent aquatic plants and their roots, in winter on the bark of a variety of deciduous trees. They prefer ashes, poplars, alders, birches, willows, and mountain ash but may feed on other species. Beavers eat their food in or near the water. In the fall they gather supplies to consume in their lodges.
European Beaver uses its flat tail as a rudder in the water. HS.
Beavers live in family groups comprising a male and female and their offspring. They live in territories which they mark with scent. They are most easily seen early in the morning and at dusk, but can be active the entire day if left undisturbed.
The beaver is a mammal that leaves some of the clearest tracks and signs; they are hard to miss on most occasions. Felled trees, cone-shaped stumps, gnawed branches and trunks as well as the beaver’s dams and structures are all highly visible.
In Denmark, beavers were exterminated 2,000–2,500 years ago, but they were reintroduced in the Holstebro area in 1999. At that time, 18 animals were released; the population has now grown and spread to the other water bodies in western Jutland, and now also in Seeland. Beavers were almost exterminated across Europe, but thanks to successful reintroduction, they are now no longer threatened in many countries.
Beaver tracks in sand; on the left, a particularly clear impression of a front foot. NPHH.
The front foot has five long toes lacking webbing as well as strong, sharp claws; the tracks, however, often show only the prints of four well-splayed toes. The footprints are 5–6 cm long and 4.5 cm wide. The hind feet have webbing between the toes. The second toe has a double claw which the beaver uses to groom its coat. The prints are 15–18 cm long and 10 cm wide.
On land, beavers move slowly and carefully. On soft ground you can often see drag marks left by the tail that can erase the footprints (cf. p. 141). The stride is 40–60 cm.
Beavers feel safe in water and avoid going on land whenever possible. For this reason, they dig narrow channels in low-lying, marshy areas where they can carry branches to their feeding sites, lodges, and dams.
Beavers fell trees to gather branches for their constructions and dams, but also to gather leaves and bark to eat. They can fell trees up to 0.5 m in diameter by means of cross-cutting, leaving only a conical stump. The largest gnaw marks are found on the side of a trunk facing water, which is why the trees they gnaw almost always fall in the water.
Beavers set their upper teeth solidly in the tree and then chew out large chips perpendicular to the grain with the lower teeth. Chips 3–4 cm wide and 10–12 cm long lie in large piles next to the tree stumps.
Near the water and in front of felled trees you will often find gnawed branches, so-called beaver-staves. The tooth marks in the trunks and branches are about 8 mm wide.
Beavers can push their lips behind their teeth, preventing water from entering their mouths while they chew. LGA; inset, ME.
Felled trees with large wood chips and a tree trunk with gnaw marks. There are clearly recognisable gnaw marks on the young tree below. LG above; Biopix below.
A beaver family living in running water will build a dam out of branches and trunks, placing it downstream and close to the lodge. The dam is sealed with sod and smaller materials to ensure a high water level in front of and around the lodge. Dams are constructed mostly in the autumn and enlarged and improved every year; they can be up to 100 m long and 2 m high.
Beaver families live in constructions resembling flat pyramids with a diameter of up to 15 m and height up to 2 m. When beavers build structures in embankments, they might be long and flat, but if the structures are in the water, they are always cone-shaped. Sod and earth are packed between branches and trunks to protect the lodge, and older structures can be completely overgrown with plants as a result. The entrance is always located below the water’s surface. Inside the lodge, you may find several chambers. In autumn, beavers stockpile branches in front of the lodge, embedding them in muddy ground.
Some beavers do not build lodges in the open but are content with building a den into a steep embankment.
In summer, beavers feed mostly on aquatic plants, their favourite being blue pygmies and their roots. You can see the remains of meals floating in the water. In autumn and winter, beavers feed mostly on the bark of ash and willow, but they also consume the bark of birch and other deciduous trees; they avoid conifers. Tree stumps may be totally peeled of their bark; chewed-off branches—‘beaver staves’—can be found in the water.
Beaver scat is brown, almost round, about 2 cm thick and 2–4 cm long. It consists of rough, undigested plant fibres. The scat is left in the water and can frequently be found near feeding sites on the shore or close to the family home.
Beavers relish succulent aquatic plants. HS.
Beavers build their lodges in embankments and open areas. AK.
Beavers leave their scat in the water.
The European Beaver may build its lodge in an embankment. AK.
The beaver family marks its territory with castoreum, a strong-smelling scent secretion produced by two glands at the base of the tail. The beaver also has two anal glands. Both castor sacs and anal glands are used to mark territory; secretions are usually left on small piles of material gathered by the animals and left near the water’s edge. Scent markings may also be left on felled trees.
The tracks of a beaver tail across a gravel path. PB.
