Eurasian beaver (Castor fiber)
|Also known as:||beaver, European beaver|
|Size||Head-body length: 80 - 120 cm (2)|
Tail length: 25 - 50 cm (2)
|Weight||11 - 30 kg (2)|
The Eurasian beaver is classified as Least Concern (LC) on the IUCN Red List (1)
One of the largest rodents in the world (3), the Eurasian beaver (Castor fiber) is also one of the most industrious mammals in Europe (4). It is well adapted to fulfil its role as a vital engineer of wetland habitats, with a broad torso and widely spaced, stubby legs which are ideal for building dams (5), and large, well-developed incisors which are efficient at gnawing the wood required for this construction (5). The front paws of the Eurasian beaver are small, dextrous and have well-defined claws, while the hind feet are webbed for swimming (5).
The Eurasian beaver has developed several other adaptations for its semi-aquatic lifestyle. The broad tail, which is covered in scaly black skin made from modified hair, is similar to a paddle blade and is used as a rudder while swimming (4). The dense underfur and long, course guard hairs not only provide protection against the cold, but can also be waterproofed by the beaver (5) (6). Waterproofing oil produced in glands is spread through the Eurasian beaver’s coat as it grooms its fur (5). This oil, along with that produced by the castor sacs, produces a distinctive, musky odour used for communication between the sexes (5).
The Eurasian beaver is also able to close its nose and ears while underwater (4), and a transparent nictitating membrane serves as a protective eyelid when it is swimming (4) (5). Furthermore, inner lips directly behind the teeth allow the beaver to use its teeth underwater to gnaw tree limbs without flooding its mouth with water (4).
The Eurasian beaver is distributed across a remarkably broad range. From Norway and Denmark in the north-western corner of Europe, its range extends eastward through Germany to Lake Baikal and Mongolia in central Eurasia (2), and from the Scandinavian Peninsula in the north to the Alps in the south (2).
The semi-aquatic Eurasian beaver inhabits gentle streams, rivers, lakes and swamps. It generally favours freshwater habitats that are surrounded by woodland, but may sometimes use a river or stream flowing through agricultural land or even urban areas (1).
Dam construction and lodge-building are probably the most familiar aspects of beaver behaviour. The Eurasian beaver builds a dam to create an area of still, deep water, relatively safe from terrestrial predators, where a ‘lodge’ can be constructed (5). The dam also provides an area where building materials and food supplies can be kept from washing away (3). The dam is built from branches, which the beaver obtains by using its chisel-like incisors to chip away at a tree trunk until it falls (3). The beaver then cuts the tree up and drags or pushes the timber to the dam site (3). Most dams measure around 22 metres in length, although some can extend for up to an incredible 600 metres (3).
A beaver lodge consists of a pile of logs, branches and sticks, compacted with mud and stones to create thick, well-insulated walls. Measuring up to 11 metres wide and 2 metres tall, the lodge comprises a central chamber above the water level, one or more tunnels leading to underwater exits, and a vertical ‘chimney’ to regulate the internal temperature (6).
In some areas, the Eurasian beaver shelters in a burrow dug into a bank instead of a lodge (3). The burrow may extend for over ten metres back from the entrance, which is situated at or below the water level (3).
As a largely nocturnal animal, most of the Eurasian beaver’s construction behaviour, as well as foraging, is undertaken during the night, but occasionally a beaver may be active in the afternoon (3). The Eurasian beaver feeds on the bark, twigs, roots and leaves of deciduous trees and shrubs, such as willow, alder, birch and aspen, as well as on aquatic plants. Prior to winter, the beaver stores sticks and logs in underwater piles. This store of food sustains the beaver through the winter months when it is less active (3).
Due to its role in maintaining the structure of an ecosystem, the Eurasian beaver is recognised as a ‘keystone species’. By constructing dams, the beaver creates new ponds and lakes, allowing many other animals and plants to converge on the area to take advantage of the new habitat (5).
Adult Eurasian beavers mate for life and provide the necessary foundation for a stable family structure. The adult male and female typically live in a small family group with the young from the past two years. Each family occupies a small, distinct territory around the shared lodge or burrow (2).
The Eurasian beaver typically mates in the winter, in January or February, and the young beavers, known as kits, are born in April or June (2) (3). The Eurasian beaver has one litter per year, with litter sizes ranging from one to nine kits (3). The young are nursed by the female for around three months (3), and may stay with the adults for up to two years (2), at which point they become sexually mature and leave the family group (3).
During the late 19th and early 20th centuries, the Eurasian beaver was wiped out in many parts of Europe as a result of overhunting and a loss of suitable wetland habitat (1) (7). The beaver was hunted for its meat, fur and ‘castoreum’, the secretion from the scent glands (1). Fortunately, a combination of conservation measures and reintroductions has resulted in the beaver returning to much of its former range, and a number of its populations are rapidly expanding (1).
Today, there are no major, widespread threats to the Eurasian beaver (1), although its populations are being impacted by a number of factors in some areas. For example, in Finland and north-west Russia, competition with the introduced American beaver (Castor canadensis) may pose a threat, and in Mongolia, the Eurasian beaver may be threatened by illegal hunting (1). Other potential threats include collisions with road traffic, habitat loss, and the pollution of streams and rivers (1).
In addition, the Eurasian beaver may come into conflict with landowners in some areas, who consider the Eurasian beaver a nuisance as it can do damage to crops and forestry. This damage trends to be less severe than that caused by other species, but is noticed because beavers are an unfamiliar presence in many areas (1) (7).
Since the Eurasian beaver’s dramatic decline in the early 20th century, numerous conservation measures have contributed to its recovery in Europe. These include hunting restrictions, reintroductions and translocations, and habitat protection (1).
Many of these conservation measures in Europe are ongoing, to prevent another decline in the Eurasian beaver population. However, in Asia, Eurasian beaver populations are considered to be more threatened and require more extensive conservation measures (1).
It has been recommended that public education and viewing opportunities should form a key part of conservation measures for the Eurasian beaver, as they could benefit the local economy through wildlife tourism, and promote positive attitudes towards this charismatic rodent (1).
Find out more about the Eurasian beaver and its conservation:
WildCRU - Conservation and Management of the Beaver:
Trees for Life - Beaver (Castor fiber):
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- Castor sacs: the glands situated at the base of a beaver’s tail. The glands secrete castoreum, a substance used to mark territories and attract mates.
- Deciduous: a plant that sheds its leaves at the end of the growing season.
- Glands: organs that make and secrete substances used by the body.
- Guard hairs: in some mammals, long, coarse hairs that protect the softer layer of fur below.
- Incisors: the front or cutting teeth.
- Nictitating membrane: a thin, tough, transparent or translucent membrane, or ‘inner eyelid’, found in various species of birds, reptiles, amphibians and fish, but less common in mammals. The nictitating membrane can be drawn across the eye to protect it from damage, or to moisten the eye whilst maintaining vision.
- Nocturnal: active at night.
- Territory: an area occupied and defended by an animal, a pair of animals or a colony.
- Translocations: the movement of a species, by people, from one area to another.
IUCN Red List (November, 2011)
- Macdonald, D.W. (1984) The Encyclopedia of Mammals. Facts on File, New York.
- Nowak, R.W. (1999) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore, Maryland.
- Coles, B. (2006) Beavers in Britain’s Past. Oxbow Books, Oxford.
- Allred, M. (1986) Beaver Behavior: Architect of Fame and Bane! Naturegraph Publishers, Happy Camp, California.
- Burton, M. and Burton, R. (2002) International Wildlife Encyclopedia. Marshall Cavendish, New York.
- Hartman, G. (1999) Beaver Protection, Management, and Utilization in Europe and North America. Kluwer Academic/Plenum Publishers, New York.