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Today on Animal Fact Files we’re discussing North American river otters. Also known as the northern river otter, this mustelid gets both its scientific and common name from where it lives. These mammals live in North America. Go figure! North American river otters are found throughout almost all of Canada, as well as the Great Lakes region and coasts of the United States. They were previously hunted across their range, drastically reducing their numbers, however, reintroduction efforts have seen them return to some parts of their historic range. This is why the range map shown is more of a general idea than representative of how things currently exist. It changes over time!

North American river otters are semi-aquatic mammals, and thus require water in their habitat. These vertebrates prefer slow-moving, clean water systems with plenty of vegetation. They have big, webbed feet, with five toes per foot that they use to navigate underwater. These webbed feet are one of the characteristics that set them apart from other mustelids like martens and badgers. River otters also have short, glossy fur and long, tapered tails which can help differentiate them from sea otters with whom their range can overlap. It's not unheard of to witness a river otter living in a coastal environment like a brackish water estuary! River otters and sea otters can be told apart by their tails: the sea otter's tail is shorter and less tapered. 

Otter fur locks in air to keep them insulated. If you've ever seen these animals swimming, you've likely witnessed the bubbles that form around them while they swim. They also have a thick layer of blubber which helps them stay warm even in the coldest water. North American river otters don't dig their own burrows, instead they use natural dens like the holes formed by root systems and caves or the burrows of other animals. In fact, river otters sometimes even live right alongside beavers in their lodges! During the summer, northern river otters are more nocturnal, but they'll come out during the day the closer the season is to winter.

North American river otters are carnivores and their diet consists mostly of fish, but they also eat frogs, crustaceans, molluscs, birds and their eggs, as well as fruit. They have thick, sensitive whiskers which help them find meals. In size, these mammals reach about twenty pounds (9kg) in weight and four feet (122cm) in length, though males are larger than females and they can bulk up even more! At least a third of their length can be attributed to their strong, muscular tail which helps them move around underwater. 

These otters are generally top predators in their habitat, but they do have a few threats to avoid. Cougars, bobcats, coyotes, alligators, crocodiles, and even killer whales all snack on North American river otters if given the opportunity! Their greatest threat, however, is humans. Apart from shootings, river otters also face trapping, and traffic where they end up as roadkill. If they can avoid this fate, northern river otters can live to thirteen years old in the wild, though more than half don't make it past their first year of life.

North American river otters can be found solitary or social. If they're in groups, it's often either a family group of a mother and her offspring, sometimes some unrelated juveniles as well, or a bachelor group of males. Male river otters don't help raise their young. These animals mate in the late winter and early spring. Their gestation period only lasts about 62 days, the same as a coyote, but the female river otters delay implantation for almost a year, so the babies aren't born until the early winter or spring of the following year. For this reason, river otters are believed to give birth only semi-annually at most.

There are typically two to four baby otters in a northern river otter litter. They have full fur, but closed eyes upon their birth. It takes nearly eight months to learn the ropes of life before they're ready to set off on their own. While females have been documented mating between the ages of one and two, it typically takes about two years before they're reproductively mature, and males usually have to wait five to seven years before they're tough enough to establish themselves as proper partners.

Northern river otters aren't typically considered territorial. They relieve themselves in communal latrines and rub their oils around their home to let other otters in the area know they're there, but confrontations are considered rare. When they swim, both their eyes and ears close up, preventing water from entering. While they don't migrate, they can move around their environment quickly, reaching swimming speeds of seven and a half miles per hour (12km/h). They can hold their breath for four minutes while they dive up to just over 60 feet (18m) deep, either for food or just to play. Others are known for their playful antics!

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