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Mammals
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mammals-otter

Northern River Otter

The northern river otter (Lontra canadensis, formerly Lutra canadensis) is a semi-aquatic carnivorous mammal in the Mustelidae or “weasel family” which includes weasels, minks, ferrets, wolverines and badgers. They live along inland and coastal waterways of North America, predominantly in the Atlantic States, Gulf of Mexico and Pacific Northwest. In Virginia, river otters inhabit a variety of habitats along rivers, lakes, streams, marshes and coastal shorelines. Otters are mostly active at night, or at dawn or dusk, but can be out and about during the day as well, especially in colder months.

River otters range from 10-25 lbs, with males larger than females. Their streamlined bodies range from 26’-42”, with long, tapered tails comprising about a third of their total body length. Their short, thick, water-repellant fur varies in color from light brown to almost black, usually with silvery brown fur at the throat. Supremely adapted for an aquatic lifestyle, river otters have a powerful, rudder-like tail and webbed feet. Able to close off their nostrils and short ears while swimming, and having additional eye covers called “nictitating membranes” that act like “swim goggles” to protect their eyes, otters can swim underwater for up to 4 minutes, swim at speeds up to 6-7 mph, and dive as deep as 55 feet. On land, otters can run, walk, bound and slide on icy or muddy slopes.

River otters are carnivorous predators equipped with sharp teeth making them well suited to catch and eat slippery fish as well as other prey including frogs, turtles, crayfish, aquatic insects, and occasionally, small birds and mammals. Sturdy molars give them the ability to crush mollusk shells as well. To capture prey, an otter relies on its good senses of smell and hearing, but underwater, it uses its long sensitive whiskers to help it find food.

River otters have few natural predators in water, but have been known to become prey for alligators. On land, otters are vulnerable to bobcats, mountain lions, coyotes and domestic dogs. Humans pose a threat to otters by causing habitat loss through urbanization, pollution of waterways, trapping, illegal shooting, and death by motor vehicles. In some areas, once thriving otter populations have disappeared; however, reintroduction programs in Midwestern states have met with success.

River otters tend to be more solitary than social. Males and females only come together during mating season, which occurs from December through April. After a two-month gestation, females give birth to 1-6 young, with an average litter of 2-3 kits. Kits are weaned at about 3 months old, but usually stay with the female for 6-12 months. Some social groups may contain the female, her young as well as yearlings and unrelated adults. Noted for their sense of play, it is mostly younger otters that “play” by wrestling and chasing as a precursor to learning adult survival and hunting skills. Males disperse to live by themselves or in male social groups. Otters in social groups hunt, travel and den together. An otter’s den is called a “holt,” which is usually an abandoned den made by another animal such as a beaver or woodchuck, or can be a natural hollow. Otters are not especially territorial and home ranges often overlap, males generally have ranges larger than female ranges. Otters use scent marking via feces and urine as a form of intergroup communication. Otters normally live about 8-9 years in the wild and have been known to live as long as 21 years in captivity.