Beavers (Castor spp.), who are famous for chopping down trees with their sharp teeth to create their well-known dams, are well-adapted to many aspects of their watery world. This includes many physical traits as well as senses sharpened especially for water living. Believe it or not, beavers may hear better under water than they do on dry land.
Beavers have sharp front teeth that they use for gnawing down trees. The inside of these teeth wear down more quickly than the outside, which keeps teeth consistently sharp, and like many rodents, these teeth grow throughout beavers’ lifetimes. Their hind feet are webbed to provide flipper-like appendages to help propel them through the water, and their fur is thick and waterproof. Their heavy tail is used as an alarm mechanism; when they smack it on water, it signals danger to other beavers. It also helps them balance on land and navigate in water.
Beavers have an excellent sense of hearing, and because they can identify a wide range of sounds, they are able to classify noises that indicate predators or other members of their social group. They hear excellently both on land and under water. Since hearing depends on the successful transmission of sound waves through a medium, and water is a much better medium than air for conducting sound, they may even hear better under water that above it.
Beaver ears look like small flaps of skin perched high on the sides of their head and almost lost in their thick fur. Because beavers spend so much time under water and their inner ears are sensitive like other animals, they have a flap that covers their ear canals when they submerge. Though the outsides of their ears are small, helping to keep water out, they have relatively large organs inside the ear, which accounts for their sharp hearing.
Despite the importance of hearing to beavers and the accuracy of this sense underwater, they probably rely more heavily on their sense of smell than anything else. Smell helps them to find food, stick together with other members of their colony, and figure out when predators are near. Their eyesight is relatively poor, though they do have a clear inner eyelid, or nictitating membrane, that they can slide over their eyes when they are swimming under water for protection and better vision.
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