Classification and Range
Otters belong to the family Mustelidae, which also includes badgers, mink, martens, skunks, weasels and wolverines. Otters are classified under the subfamily Lutrinae, which has a total of 13 species in six genera.
North American river otters are found throughout Alaska, Canada and the contiguous United States.
North American river otters live in a variety of habitats, but they spend most of their time in or near streams, rivers, lakes and marshes. They often build a den or a burrow in their home territory. They will if necessary, however, travel great distances over land and through water to find food.
Adult length, with tail: 2.5-5 feet (76-152 cm)
Adult weight: 10-30 pounds (4.5-13.6 kg)
They live 8-10 years in the wild. Their life span in captivity is 18-20 years.
In the wild: Birds, crabs, crayfish, fish, frogs, rodents, turtles, and aquatic invertebrates. Otters eat whatever is readily available and easiest to catch.
At the zoo: Trout, chicken parts, horsemeat and occasionally commercially prepared trout chow.
Otters sexually mature at about 2 to 3 years of age. Mating occurs in the fall or spring, with birth taking place the following year. North American river otters have a delayed implantation cycle, which differentiates them from any other related otter species. Although gestation takes only 60-63 days, the total period of pregnancy can vary from 245-380 days. Pups are born in April or May. Two or three young are born in a secluded den. However, litters may range from one to five pups. Females rear young alone.
Otter pups weigh about 4.5 ounces (128 g) when born. Pups nurse for three to four months, and begin to swim two months after birth. Young otters swim naturally, but the mother must coax them into the water for their first swim. During the first days of swimming, a pup often climbs onto its mother's back. Pups leave their mother when they are 1 year old, and ready to look for their own territory.
Otters have adapted perfectly to an aquatic life-style. They are well suited to swim and dive, and their slippery hydrodynamic form exemplifies the perfect adaptation to an amphibious way of life. Otters have webbed feet, with small dexterous front feet and large, powerful hind feet. The muscular tail is thick and flat at the base, tapering to a point. Otters use their hind limbs and undulating movement of their tail as the main source of propulsion through water, but they may also use their forelimbs for paddling.
All otters have sleek, waterproof fur. The hair is short, dense and soft. Otters have excellent vision, especially under water, which helps them catch prey. Stiff whiskers, which are sensitive to water turbulence, are another adaptation to finding prey in muddy or dark waters. The thumbs on the front paws show freedom of movement, and can be opposed when picking up, holding small objects or assisting in eating their prey.
Unlike other species of otter (notably the well-known sea otter), North American river otters and other "webbed-footed" otters catch prey with their mouths versus their feet. Although otters are quick swimmers, their skill is shown better in their ability to maneuver rapidly, which helps them chase down their prey. Additionally, otters have an accelerated metabolism that gives them seemingly endless energy, but it also means that they must hunt and feed frequently.
Slippin' and a Slidin'
Although otters forage mostly in the water, they are equally at home on land, and can run quickly. When otters move on land, they bound in a loping fashion, with their backs arched. Whenever possible, otters combine running with a slide in the mud, ice or snow. This has added to their reputation of being the most playful of the Mustelidae. Otters are also very vocal, and communicate to one another with a large variety of calls, such as whistles, buzzes, twitters, staccato chuckles and chirps.
As they mature and become solitary, otters use scent marking to distinguish territorial boundaries. Otters have a pair of scent glands at the base of their tail which gives them a heavy, musky smell. Scent marking also communicates identity, sex and sexual receptivity. A male can follow the scent markings of a female in estrus for over 5 miles (8 km) during the breeding season. Although they can be tolerant of other otters, males do compete for breeding privileges. There is little overlap of territorial boundaries between adults of the same sex. However, a male's territory may overlap the territories of several females.
Location at the Zoo
Woodland Park Zoo's North American river otters are located in the Taiga Viewing Shelter of the Northern Trail. The otter exhibit allows visitors an up-close observation of the feeding habits and swimming abilities of otters. Also in the Taiga Viewing Shelter, visitors can see brown bears frolicking in the water. Other animals that can be seen along the Northern Trail are wolves, mountain goats, bald eagles and elk.
Excessive fur trapping is the single greatest threat to all otter species. As recently as the mid-1980s, over 30,000 pelts were taken each year for the valuable skin of the North American river otter. Hunting of other otter species continues worldwide. All otter populations continue to decline as a result of water pollution, overfishing of commercial stock and habitat destruction. Today, all otter species are considered threatened, while at least five of the 13 otter species are listed as endangered. Although the North American river otter is not an endangered species, its population has been severely reduced or eliminated from much of its range. However, since 1976, efforts have been made to reintroduce the North American river otter into several of the interior states of the U.S. Nevertheless, as their numbers continue to decrease, the future existence of all species of otters in the wild is in jeopardy.
How You Can Help!
Woodland Park Zoo is helping to contribute information to the captive breeding, husbandry and public awareness of this captivating native species. The effort to save animal species requires cooperation and support at the international, national, regional and individual levels. You can help in this cause. Join and become active in Woodland Park Zoo and other conservation organizations of your choice. Please do not buy products made from wild animal parts.
Contact Woodland Park Zoo at firstname.lastname@example.org find out other ways you can support conservation programs at the zoo. Learn other ways you can help conserve wildlife and the habitats they require for survival by visiting our How You Can Help page.
Sources and Suggested Reading
Chanin, Paul. 1985. The Natural History of Otters. Facts on File, New York, NY. 179 p.
Esbensen, Barbara. 1993. Playful Slider/The North American River Otter. Littlebrown, Waltham, MA. 32 p.
Tulloch, Bobby. 1994. Otters. Voyager Press, New York, NY. 48 p.