Beaver biology
the second largest
rodent in the world
Learn about the biology of a beaver
What are beavers?
Beavers are large rodents with adaptations for the aquatic environment:
- They have short limbs and their hind feet are large and webbed for propulsion in the water, whilst the front paws are dextrous for manipulating food and building material. They can carry remarkably heavy objects such as stones by tucking them under their chin, holding them with their front paws, and walking for short distances on their hind legs.
- Their tails are flattened from top to bottom and hairless, and they have multiple uses: as a rudder when swimming (multiple muscle groups enable beavers to rotate their tails in different directions); to slap on the water surface as an alarm to other beavers when they sense danger; and as a prop when walking on their hind legs for short periods.
- Beavers’ fur consists of an outer layer of coarse, long guard hairs, each measuring 5-6cm long, and an inner layer of shorter (2-3cm), softer underfur. The underfur is very dense – between 12,000 – 23,000 hairs per square centimetre – and when beavers submerge, it traps a layer of air to keep them warm. They spend a lot of time grooming in order to keep their fur clean, using a specially adapted grooming claw (split in half, so that they can run the hairs through the middle).
- Beavers have whiskers which they use to detect objects in dark or murky water, as well as indicate the strength of water currents. Their eyesight is poor, so they rely mostly on hearing, touch, and smell.
- Other adaptations include: nostrils set higher on the head than other rodents; dense hair inside their ears to prevent water entry; and an additional, transparent eyelid – the nictitating membrane – to enable vision underwater.
- The beaver’s skeleton is larger than that of other mammals of a similar size, and their skull and jaw bones are particularly robust in order to support the strong facial muscles needed to gnaw and process trees. They have a clear sagittal crest (a ridge on the top of the skull) to which strong jaw muscles are anchored.
- Beavers have large incisor teeth which grow continuously throughout their lives to counteract the wear caused by gnawing trees. There is a large gap between their incisors and their molar teeth, and they have a second set of lips which they can close within this gap. This enables them to gnaw underwater and carry sticks in their mouth whilst swimming without swallowing water.
Beavers are entirely herbivorous
They eat a mixture of shoots, leaves, bark, understorey and aquatic plants. Their favourite tree species are aspen and willow, and understorey plants consumed include brambles and ferns. Their digestive system contains a large number of microorganisms and flukes and worms which help them to digest their nutrient-poor diet, and they also reingest some of their faeces to extract a greater percentage of the nutrients from their food.
Beavers are monogamous and a pair typically have 2 or 3 kits each year, after a gestation period of just over 100 days. Kits typically disperse when they are around 2 years old, but only breed when they are 3 years old.
Beavers live in burrows or lodges. To construct a burrow, they dig into the riverbank below the water level and then excavate upwards to create an air-filled chamber. To construct a lodge, they break through the roof of the chamber, pile sticks and mud on top, and hollow out the pile from the inside. A beaver family can have multiple lodges and burrows within their territory, and territory is marked using scent glands.
To find out more about beavers, like why the build dams, how many species of beavers there are and more, head to our beaver landing page and scroll down to the frequently asked questions.
