North American River Otter

River otters mostly rely on aquatic organisms for food, including fish, amphibians, crayfish, and other invertebrates. Occasionally, they will prey on birds, small mammals, and aquatic plants. Diet depends greatly on the region and season. Otters hunt by sight and touch. They use their long whiskers or forelimbs to detect prey in dark or murky waters. Prey is captured with the mouth and eaten immediately, usually in the water, although larger prey is eaten on land. They may hunt in small family groups, herding fish towards the shore or each other.

At the Zoo, otters receive a specialized ground carnivore diet, lake smelt, capelin, and trout.

Before European colonization, the river otter was one of the most widely distributed mammalian species in North America. Historically, they inhabited a range of coastal and inland aquatic habitats from arctic Alaska and northern Canada to the southern USA. By the mid-1950s, populations were eliminated through many parts of their range, especially around heavily populated non-coastal areas of the USA and southern Canada. Population trends have stabilized in recent years with reintroduction and conservation efforts resulting in reoccupying areas where they were previously eliminated. Northern American river otter populations are still considered vulnerable or imperiled throughout much of their range in Midwestern United States and the Appalachian Mountains.

River otters are found along streams, rivers, ponds, lakes, reservoirs, and in saltwater marshes – basically any habitat where there is a permanent food supply and easy access to water. River otters can tolerate a variety of environments, including cold and warmer latitudes and high elevations. In many areas, they occur in close association with American beavers, whose ponds provide prey and areas to den. North American river otters seem to be sensitive to pollution and disappear from areas with polluted waters.

Natural predators of river otters include bobcats, birds of prey, alligators, and other large predators.

Although trapping is legal in many areas, unregulated harvesting for fur is a threat in some regions in the U.S. Water pollution, including man-made debris and chemicals, reduces the availability of prey and increases toxin levels that can negatively affect reproduction rates. In coastal areas, oil spills are the most severe threat to local river otter populations.

With their streamlined body, river otters are perfectly suited for life in the water. They have short, webbed paws that propel them forward through the water. Their muscular, rudder-like tails allow quick movement and change of direction while swimming. Their fur is a rich brown with a grayish upper chest, throat, and chin. Otters can keep themselves warm while swimming by trapping air between their body and fur. This air pocket is heated up by the otter's body heat and creates a buffer between the water and the otter. As you watch them swim, you'll notice a lot of bubbles, which is the warm air escaping. After swimming, otters need to groom their fur to re-trap the lost air and prepare for their next swim. Their noses are not covered in fur but are surrounded by sensitive whiskers, or vibrissae, which help them feel changes in the environment. The river otter’s eyes are on top of its head to allow swimming at the surface. An additional eyelid called the nictating membrane, allows the otter to see when underwater. Their ears and nostrils close when submerged. Sharp canines help them grab and kill prey quickly underwater.

Male and female river otters do not associate except during the mating season. Males will often breed with several females whose home ranges overlap with their own in late winter to early spring, depending on the region. Gestation lasts two months, but the young may be born up to a year after mating because these otters employ delayed implantation of the fertilized egg in the uterus. Births of an average of two to three young occur from February to April in a den near water. Offspring are born with fur, but blind and toothless. Their eyes will open at about one month of age and they are weaned off mom’s milk at about three months old. Young otters will begin to leave their birth range between six months and a year. Sexual maturity is reached after 2 years of age.

Like other mustelids, otters have musk glands near the base of their tails that they use to communicate and mark their territories. These glands produce a very strong, musky odor that, combined with urine and fecal latrines, sends a strong signal to others. River otters are very vocal and communicate with a large variety of calls, such as whistles, buzzes, twitters, staccato chuckles, and chirps. They also use touch and communicate through posture and other body signals.

North American river otters get their boundless energy from their very high metabolism, which also requires them to eat a great deal each day. For most of the year, the otter is most active from dusk to dawn, but may be more commonly seen during the day during the winter months. Individuals live alone or in family groups, typically females and their young. They typically travel in water and can swim long distances under ice during the winter, staying submerged for up to four minutes and swimming up to seven miles per hour! River otters can travel long distances on land from one water source to another. On land, otters often slide on their bellies and push forward with their back legs, especially in the snow or on slippery banks. This sliding behavior, as well as other activities seen as “play”, serve a purpose. Some are used to strengthen social bonds, practice hunting techniques, and scent mark.