North American river otters are semi-aquatic mammals, with long, streamlined bodies, thick tapered tails, and short legs. They have wide, rounded heads, small ears, and nostrils that can be closed underwater. Their whiskers are long and thick. The fur is dark brown to almost black above and a lighter color ventrally. The throat and cheeks are usually a golden brown. The fur is dense and soft, effectively insulating these animals in water. The feet have claws and are completely webbed. Body length ranges from 889 to 1300 mm and tail length from 300 to 507 mm. Weight ranges from 5 to 14 kg. Males average larger than females in all measurements.
North American river otters occur throughout Canada and the United States, except for areas of southern California, New Mexico, and Texas, and the Mohave desert of Nevada and Colorado. In Mexico they are found in the delta areas of the Rio Grande and Colorado river. Otters were locally extirpated from portions of their range but reintroduction and conservation efforts have helped stabilize populations. (NatureServe, 2008)
North American river otters are found anywhere there is a permanent food supply and easy access to water. They can live in freshwater and coastal marine habitats, including rivers, lakes, marshes, swamps, and estuaries. River otters can tolerate a variety of environments, including cold and warmer latitudes and high elevations. North American river otters seem to be sensitive to pollution and disappear from areas with polluted waters.
North American river otters build dens in the burrows of other mammals, in natural hollows, such as under a log, or in river banks. Dens have underwater entrances and a tunnel leading to a nest chamber that is lined with leaves, grass, moss, bark, and hair.
Males and females only come together during the mating season. Males usually mate with several females that live in or near their own territory.
Males and females come together to breed in late winter or early spring. Pregnancy lasts two months, but the young may be born up to a year after mating because these otters delay the implantation of the fertilized egg. Births occur from November to May, with a peak in March and April. Females give birth to from 1 to 6 young per litter, with an average of 2 to 3, in a den near the water. They are born with fur, but are otherwise helpless. They open their eyes at one month of age and are weaned at about 3 months old. They begin to leave their mother's home range at from 6 months to a year old. Sexual maturity is reached at 2 to 3 years of age.
Females give birth to, nurse, and care for their young in a den near the water. The young are weaned at about 3 months old and begin to leave their mother at 6 months old.
North American river otters can live up to 21 years in captivity. They normally live about 8 to 9 years in the wild.
North American river otters live alone or in family groups of, usually, females and their young. They are known as playful animals, often seen sliding in mud and snow and playing in the water. Many "play" activities actually serve a purpose. Some are used to strengthen social bonds, to practice hunting techniques, and to scent mark. North American river otters get their boundless energy from their very high metabolism, which also requires them to eat a great deal during the day.
They are excellent swimmers and divers, able to stay underwater for up to 8 minutes. They are also fast on land, capable of running at up to 29 km/hr. These otters normally hunt at night, but can be seen at all times of day.
River otters have large home ranges, with one otter on every 2 to 78 kilometers of waterway. Home range sizes vary considerably and seem to depend on the richness of food resources and habitat quality. Despite these large ranges, river otters are only slightly territorial and generally practice mutual avoidance.
North American river otters communicate in a variety of ways. They vocalize with whistles, growls, chuckles, and screams. They also scent mark using paired scent glands near the base of their tails or by urinating/defecating on vegetation within their home range. These glands produce a very strong, musky odor. They also use touch and communicate through posture and other body signals.
North American river otters perceive their environment through vision, touch, smell, and hearing. Their large and abundant whiskers are very sensitive and are important in tactile sensation. These whiskers are used extensively in hunting, as smell, vision, and hearing are diminished in the water.
North American river otters eat mainly aquatic organisms such as amphibians, fish, turtles, crayfish, crabs, and other invertebrates. Birds, their eggs, and small terrestrial mammals are also eaten on occasion. They sometimes eat aquatic plants.
Prey is captured with the mouth, and mainly slow, non-game fish species are taken, e.g., suckers. The otter's long whiskers are used to detect organisms in the substrate and the dark water. Prey is eaten immediately after capture, usually in the water, although larger prey is eaten on land.
North American river otters are sometimes taken by bobcats, coyotes, birds of prey, alligators, and other large predators. They mainly escape predation through their agility in the water and on land, their vigilance, and their ability to fiercely defend themselves and their young.
North American river otters are important predators of fish and aquatic invertebrates.
North American river otters generally do not have adverse affects on humans.
North American river otters are important parts of healthy, aquatic ecosystems.
North American river otters have been hunted for many years for their attractive and durable fur. In the 1983-84 hunting season, 33,135 otters were taken with an average selling price of $18.71 per pelt. Otters are stll an important source of income for many people in Canada and the western United States. River otters also eat "trash fish" that compete with more economically desirable game fish.
Northern river otters are listed in Appendix II of CITES. Populations were once eliminated through many parts of their range, especially around heavily populated areas in the midwestern and eastern United States. Population trends have stabilized in recent years and reintroduction and conservation efforts have resulted in recolonization of areas where they were previously extirpated. Northern river otter populations are still considered vulnerable or imperiled throughout much of their range in midwestern United States and the Appalachian mountains. They may be eliminated in New Mexico and population status in South Carolina and Florida has not yet been reviewed.
Tanya Dewey (author), Animal Diversity Web.
Eric J. Ellis (author), University of Michigan-Ann Arbor.
Kruuk, Hans. 1995. Wild Otters: Predation and Populations. Oxford University Press. 240 pgs.
Macdonald, Dr. David. 1984. The Encyclopedia of Mammals. Equinox (Oxford) Ltd. Pgs 125-129.
Nowak, Ronald M. 1991. Walker's Mammals of the World, 5th ed, Vol II. The Johns Hopkins University Press. Pgs 1135-1137.
Ulrich, Tom J. 1990. Mammals of the Northern Rockies. Mountain Press Publishing Company. Pg. 68.
Wernert, Susan J [Editor]. 1982. Reader's Digest North American Wildlife. The Reader's Digest Association, Inc. pg. 61.
NatureServe, 2008. "NatureServe Explorer: An online encyclopedia of life version 7.0" (On-line). Accessed January 23, 2009 at http://www.natureserve.org/explorer.