Adaptations to a Semi-Aquatic Life
Beavers have adaptations for living on land and in water. Webbed hind feet and a large flat scaly tail help them swim. The tail is also used to store fat and to help them thermoregulate. The pelage consists of a dense underfur and long (60 mm-65 mm) stiff dark guard hairs that help repel water. The fur helps insulate the beavers against the cold whether in the water or on dry land. When swimming a layer of air is trapped by the fur giving them a silvery appearance. Beavers moult twice a year, in the spring (April) and in the autumn (September).
Other adaptations to an amphibious lifestyle include eyes, ears and nostrils placed high on the head so they can maintain vigilance when swimming. The nostrils have special muscles that close the nose tightly when diving.
The ears too have special muscles that allow the ears to fold flat, thereby preventing water from entering. The ears are also densely furred inside; this fur traps air and stop any water seeping in. The eyes have a third, clear eyelid called a nictitating membrane that allows them to see underwater. In contrast to humans, beavers have an epiglottis at the back of the nostrils rather than in the throat; this flap of elastic cartilage prevents water from entering the windpipe when diving and swimming.