Nature Notes

Do wild animals play? Most of us are willing to believe that young wild animals might play. After all, we’ve seen pet kittens and puppies play. It’s harder to imagine adult wild animals at play. If you have doubts, consider river otters, well known for their playfulness. Over the years, they’ve become more common in our region.

You’ll usually find North American river otters (Lontra canadensis) in and around fresh water, and brackish water in coastal areas. They’re in the weasel family (Mustelidae). Keep an eye out for them in ponds, rivers, and streams. Fish are their main food. In water, river otters are top predators, meaning that they have no natural predators and are at the top of the water’s food chain (who eats whom).

What do river otters look like? They’re low, long, and sleek, weighing 10-30 pounds, and measuring 3-4 feet long, including their thick, pointed tail. They have dense, water-repellent fur and webbed feet – all the better for hunting in water. You might spot a family group of river otters frolicking in a pond, swimming, splashing, diving, chasing, and moving fast.

Their fur became a liability for river otters in the 1600s, when they were over-trapped in the fur trade between North America and Europe. By the 1800s, river otters were rare in Massachusetts.

And now? By the 1930s, they were known in western Mass, and by the 1960s could be found throughout our state. Reasons for their comeback include the clean-up of the state’s waters, reduced pollution, and more beaver ponds. Like many other wild animals, river otters also benefited from the re-growth of forests as agriculture declined in the state in the 1900s.

Although river otters are closely tied to water, they are considered semiaquatic because they also use land. They have dens in the banks of ponds and streams, typically dens dug and abandoned by other animals, or natural holes. They use areas on land as latrines. (Look for ground covered with fish scales, typically about 15 feet from the water’s edge.) Latrines also serve as “scent stations,” where otters leave scents that communicate information to others.

River otters tend to live in overlapping home ranges. They regularly travel over land and through wooded swamps to find new ponds to inhabit. This time of year – late winter, early spring – is when they’re most likely to be on the move, searching for a new place. Last year’s young also leave their families around now. On land, river otters might be prey for coyotes, bobcats, or eagles. Otters sometimes become road kill.

Land is where you’re most likely to find evidence of river otters’ most famous play – an otter slide or “belly slide.” These animals, adult or young, are known to slide on their bellies down banks of snow or mud, over and over again. They’ll slide not just to travel quickly, but, it seems, for the fun of it. What does an otter slide look like? It’s a smooth, straight, downhill path indented in snow or mud, about 8 inches wide and up to 20 feet long – made by sliding bellies.

Female river otters give birth to 2-3 young (on average) in March-April. The “pups” or “kits” stay in the den for about 2 months but then are out and about. They learn to swim and hunt from their mother and usually stay with her through the winter.

Male and female mate shortly after young are born, but the next litter doesn’t arrive until the next year. River otters have delayed implantation, in which fertilized eggs go dormant and float in the female’s uterus for many months. Eventually they are triggered, perhaps by hormones influenced by changes in daylight, to implant in the uterus and develop for about two months. Some other animals also have delayed implantation, including fishers, minks, skunks, and bears. It serves to ensure that young are born at a time that will give them good chances for survival.

If you’d like to see river otters, perhaps at play, consider visiting otter exhibits at the Blue Hills Trailside Museum, Milton, MA; Ecotarium in Worcester, MA ; or Buttonwood Park Zoo, New Bedford, MA.