(Northern River Otter)
The river otter is large for a mustelid and beautifully adapted for its aquatic habits. Its body is sleek and cylindrical, the head is small, and the tail, nearly one-third the total length, tapers into a long, rudder-type round tail. Its feet are webbed, the claws are short. The fur, among the finest of the furbearers, is very dense and dark brown, but its almost black when wet. Their fur is lighter on the sides of the head and it can be silver-gray on the underside of the head and throat. Their fur provides good insulation in the frigid waters it inhabits, and it efficiently sheds water. Their appearance is almost like a seal. A well-meaning geologist once reported seeing seals in Yellowstone Lake in Yellowstone National Park - otters are not closely related to seals, but they do have some similarities. Total length is 40 to 54 inches (1000-1346 mm), tail length is 14 to 20 inches (353-510 mm), and they weigh 10 to 30 pounds (4.5-13.6 kg).
Otters were once found throughout most of North America, but the fine, high quality of their fur made them a favorite quarry of trappers, and habitat loss from damming rivers, siltation, riparian development of all kinds led to the decimation of this species over much of the United States. Conservation and protection has accommodated it return to part of its former range. It is generally found throughout North America north of Mexico but absent from extremely arid regions of the west and southwest.
River otters are rarely found far from water. They are found along the banks of and in streams and rivers and in lakes, swamps, marshes, and beaver ponds. An Idaho study found that otters preferred valleys to mountain habitats, and stream-associated habitats to lakes, reservoirs, and ponds, and food had the greatest influence on habitat use.
They eat mainly aquatic animals, particularly fishes (mostly slow-moving, mid-size species such as suckers), frogs, crayfish, and turtles. They also prey on nesting aquatic birds in some areas as well as insects, earthworms, small mammals an even juvenile muskrats and beavers. An Idaho study reported diet items included fishes, invertebrates, birds, mammals, and reptiles.
River otters seem always on the move and they are especially known for their playfulness. They slide in mud and snow slides along river banks and seem to have great fun. They also have been observed playing with sticks in the water and even dropping pebbles to retrieve them from the bottom of the river. In the water they are agile and lithe, and can swim underwater for up to 6 miles per hour for 2 to 3 minutes. They can forage under the ice in the winter apparently acquiring air from air pockets under the ice. On land they move with a rapid undulating (inchworm) movement at a fairly rapid pace. However, give them some crusty snow or ice and they move along rapidly by alternating a series of hops with belly sliding. With this method they can achieve speeds of up to 15 miles per hour. They remain active all winter, even in fresh, deep snow. In general, they are primarily nocturnal, but may be active by day. Idaho study reported diurnal activity in winter and nocturnal activity in other seasons, with most activity in winter, and progressively less activity in other seasons. They den in hollow logs, spaces under roots, logs, or overhangs, abandoned beaver and muskrat lodges, dense thickets near water, or burrows of other animals. Their home range is typically linear; ranging from 32 to 48 km. (19-30 miles) for a pair or a male, and less for females with young. population density of 1 per 3.5 km (2 mi) of river length has been recorded. An Idaho study reported that home ranges overlapped extensively and ranged in length from 8 to 78 km ( 5 to 47 mi). Home range shape was determined by drainage patterns.
In Idaho, breeding begins in late April following the birth of a litter from the previous spring. implantation is delayed 10-ll mo, thus total Gestation lasts 9-12 months; but implantation doesn't occur until late winter. Females produce 1 litter of 1 to 5 young (average 2.4 in Idaho). The young open their eyes at about one month old, they leave the den when about six weeks old when they begin to learn to swim. Young stay with mother for about 1 year, and reach sexual maturity in 2 years.
|Status:||Protected nongame species|
Important State References:
Melquist, W.E. and M.G. Hornocker. 1983. Ecology of river otters in west central Idaho. Wildl. Monog. 83:1-60.