River otters belong to the family Mustelidae, which also includes weasels, badgers, martens, ferrets, wolverines, and mink. River otters are excellent swimmers and divers. They are able to stay underwater for up to eight minutes, using their specially adapted ears and nose which they can close to keep water out while they’re submerged. River otters are often seen playing games. They are social, commonly living in family groups made up of an adult female and her pups. Adult males are often solitary but sometimes live in small groups together. River otters live in burrows along riverbanks, usually taking over abandoned dens made by other animals such as beavers. Like the mink, these animals were a staple of the fur trade in the 1700 and 1800s. Female river otters give birth in the spring. Babies are born blind and stay in the den until they’re about one month old. Their mother coaxes them into the water where they learn to swim.