A Shedd river otter standing on a rockRiver otters take on winter the old-fashioned way—with a thick coat and gritty determination.

North American river otters, Lantra canadensis, are one of the Great Lakes animals that tough it out when winter rolls around. Unlike many other local species, they don’t migrate to a far-off place; they don’t hibernate in a deep sleep, and they don’t slow down to minimize their energy expenditure.

River otters’ two-layered fur coat allows them to stay active throughout winter. Outer hairs provide water repellency, and soft, dense underfur insulates them for adventures in and out of frigid water. River otters move effortlessly in any temperature water thanks to adaptations like an elongated body, powerful webbed feet and a tapered tail for propulsion. Also, they make their homes close to water—usually in burrows along the edges of rivers, lakes, or wetlands.

Winter may not change where river otters live, but it does change some of their daily habits. For example, they are more diurnal (active during the day) in winter, while they are more nocturnal (active during the night) in other seasons. During the winter day, when temperatures are highest, river otters may travel more to find open bodies of water where they can fish. When fish aren’t readily accessible, river otters may root out hibernating frogs and turtles  buried in the mud.

While snow and ice may slow down us humans, neither poses a problem for river otters, who don’t need sleds and skates to slide down snowy hills and across frozen ponds with ease.

If they can’t find openings in the ice for fishing, river otters might tunnel into beaver dams for access to open water. In late winter, water levels sometime drop below the ice, leaving an air space that lets them swim and hunt beneath the ice.

River otter perched on rockWinter and early spring are the time for breeding, but the females do not give birth until nearly a year later (usually from March to May). River otters, as well as sea otters, have an adaptation called delayed implantation, in which the embryo is in suspended animation as a simple ball of cells for about nine months before it implants in the uterine wall and starts to develop. Actual gestation is about 62 days. Delayed implantation allows river otters to raise their young when environmental conditions—warmer temperatures and abundant food—are most favorable for the pups’ survival.

At Shedd, you can find a river otter in our Local Waters gallery. Her name is Rio, and she is nearly 20 years old. While she may not have to worry about the cold temperatures like her counterparts in the wild, she still prepares for winter. Although Rio has lived at Shedd for most of her life, she still sheds her summer coat and grows a thicker winter coat each November and then sheds her winter fur in March or April. This is due to a mix of natural and artificial lighting in her habitat that mimics the seasonal changes outside—just like us, she knows when the days are getting shorter or longer. If Rio isn’t swimming or enjoying an enrichment session in her habitat, she is probably in her den on the far left side of her exhibit.

Whatever time of year, North American river otters are one of the most charismatic and robust animals in the Great Lakes. How are you like a river otter, “toughing it out” when winter rolls around?

—Sam Bugg, Great Lakes outreach manager