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).