While many mammals hunker down for winter, river otters remain active and rambunctious, swimming under the ice, tobogganing down snowy embankments, and bounding along streambanks and across frozen lakes searching for food.
With thick, multi-layered and virtually waterproof fur, along with snug dens to retreat to during cold nights, otters face few threats from predators or the elements. They even engineer underwater tunnels through beaver dams and beneath river banks so they can move secretly from one fishing pool to another.
Their dens, usually tunneled into river embankments, often have multiple entrances, enabling otters to enter the water without exposing themselves to predators. Once underwater, they can hold their breath for up to four minutes.
While otters prey mostly on fish, they also eat crayfish, mollusks, and insects. In winter, some may dig up hibernating frogs. During winters when fish are scarce, a few otters may die of malnutrition, though most deaths usually stem from automobile collisions, trapping and various diseases.
When fishing or hunting far from their home dens, otters curl up in a variety of sheltered resting places, including beaver lodges and hollow stumps. One 16-month study in Montana tracked a single individual to 88 different resting spots.
On the plains of Boulder County, single otters have been seen during recent winters at Boulder Creek, Walden Ponds, and Pella Ponds, south of Hygiene. These stray individuals may be young dispersing males, as otter families have not yet been reported east of the mountains. In long-term studies, young males equipped with radio collars have been tracked as far as 130 miles from their natal dens.
River otters seem to be faring slightly better in the mountains, where they’ve been seen or photographed with remote cameras while fishing in North Boulder Creek, Beaver Reservoir and Brainard Lake. These semi-aquatic members of the weasel family were extirpated from Colorado during the early 20th century. They only began to reappear in numbers during the 1970s, when Colorado Parks and Wildlife released otters into several river drainages on the Western Slope, including the Colorado River near Grand Lake.
It’s mind-boggling to envision stray otters making the trek across the Continental Divide from Grand Lake to Boulder County’s mountain lakes, but that’s apparently what’s happened. Other individuals may have migrated here from southern Wyoming and western Nebraska.
Throughout North America, river otters are slowly recovering from the slaughter inflicted by fur trappers during the nineteenth century. We’ve been pleasantly surprised to encounter families sleeping on logs in Georgia’s Okefenokee Swamp and in the Louisiana bayous, and river otters now range through at least 44 states from Alaska to Florida.
Defenders of Wildlife estimates the North American population at around 100,000, still just a fraction of the millions who likely frolicked in our lakes and rivers prior to European conquest and settlement.
It’s hard to watch or listen to river otters without smiling. While camping along Nebraska’s North Platte River in March, we often hear families twittering and chattering through the night. We imagine pairs touching noses, rolling and tumbling in the water, then shooting down to the bottom to nab a carp or two.
Stephen Jones and Ruth Carol Cushman are authors of Wild Boulder County and Peterson Field Guide to the North American Prairie.
Other November events
- Mule and white-tailed deer spar and mate.
- Swans, snow geese, and loons stop over on prairie reservoirs.
- Box Elder bugs and spiders move indoors.