Otters adapted to winter’s cold

  • The Northern River Otter is well adapted to cold winter weather. pixabay.com

For the Monitor
Sunday, January 07, 2018

Wild animals utilize various strategies for surviving harsh winter conditions.

Some of them, like some people, migrate to warmer climates.

Others, including reptiles, amphibians and a few mammals hibernate or become dormant.

But there are some species that are incredibly well adapted for low temperatures, wind and snow and remain active. One example is the Northern River Otter.

The river otter, the largest member of the weasel family, is found throughout the United States and Canada, wherever there is clear water and abundant food. They live along streams, lakes and wetlands because fish make up a large part of their diet. They also eat crayfish, frogs, turtles, insects and other aquatic invertebrates. Eating frequently is one way they keep warm, by fueling their internal furnace to maintain their relatively high metabolism.

Finding fish and other aquatic menu items can be difficult when waterways are frozen. In winter, otters spend more time near streams and rivers where the current often maintains open water. They may also den in an old beaver lodge with underwater access. River bank tunnels also offer a route to the water.

Otters are swift and graceful swimmers with four webbed feet, a streamlined body and a strong tapered tail for steering. When swimming, a clear eyelid, called the nictitating membrane, covers each eye like goggles, allowing them to see underwater. Their ears and nostrils close to keep out water. Long stiff and highly sensitive whiskers also help them feel for their prey. These tools enable them to chase and catch fish underwater. If the fish are small enough (four to six inches), they will eat them without surfacing. Larger prey will be brought on shore or into a den to be consumed. In winter, they may dig up hibernating frogs or turtles buried at the bottom of a pond.

Two layers of fur provide otters with incredible protection from the cold. A dense underfur traps warm air close to their bodies while an outer layer of waterproof guard hairs keep them dry. This fur is dark brown but can look sleek and black when they emerge from the water.

Their fur is not only protection for the otters, but early fur trappers also found it appealing. For hundreds of years and even today, otters are trapped for their soft warm pelt. By the 1800s, their numbers had declined enough that the fur trade was no longer as lucrative and so their population has rebounded in much of their historical range.

Beyond the physical adaptations that otters possess, they are also well known for their antics and playfulness. In the winter it is common to see places where the imprints from their feet stop and are replaced by a six to eight inches wide trough in the snow where the animal has flopped down on its belly and slid down a slope. They seem to do this for fun, but it is also a way to conserve energy as they are moving through their territory.

The playfulness of otters is mostly seen within family groups of a mother and her pups. She usually gives birth to two to four young in March or April. At birth they are covered with fur but their eyes are shut and they have no teeth. The young develop within the birthing den. After about five weeks they are fully active and by two months are out foraging with their mother. In spring they may slide down banks on mud or leaves instead of snow. The pups remain with their mother for seven to eight months, or until another litter is born.

As relatively social animals they communicate using various sounds including whistles, twitters, chuckles, chirps, growls and a bloodcurdling scream when they are frightened. They also use scent to communicate, leaving scent mounds throughout their territory. Hearing or seeing them is more likely in the winter since they are more active in daylight hours at this time, taking advantage of the warmth of the sun. But even if you don’t observe the actual animal, finding their slides, and tracks in the snow can bring a smile to your face and warmth to your heart on a cold winter’s day.