The playful behaviour of river otters has long enchanted animal lovers. But researchers continue to wonder about what drives these creatures’ curious antics
ANIMAL STORIES HAVE A WAY of living on. An unexpected and substantial drop in the number of snapping turtles in Lake Sasajewun is one such tale.
Researchers, led by professor Ronald Brooks from the University of Guelph, began studying the turtles in this part of Algonquin Provincial Park, near Highway 60, in 1972. The population of female turtles was stable until the mid-1980s, when in 1989 it plum- meted from 47 known adults to just 16. The cause? The team discovered that starting in the winter of 1986/87 and for three consecutive winters, river otters started killing and eating turtles hibernating in the muddy sediment at the bottom of the lake.
The known diet of river otters consists primarily of fish and crustaceans; some otters also eat molluscs, amphibians, insects and waterfowl. But digging adult snapping turtles out of lake bottoms in the middle of winter? That was a new one.
Three decades after the Lake Sasajewun findings came to light, the story remains top of mind for otter experts trying to illustrate the creatures’ intelligence and curiosity. “At least one otter somehow figured out that’s where turtles are in winter and made a specialty of finding them,” says Don Reid, a zoologist with Wildlife Conservation Society Canada who has studied otters extensive- ly during his 40-year career. The otters had learned a new way of getting food, he says.
River otters are an enigma hiding in plain sight. A semi-aquatic species, they are members of the mustelid family, which includes mink, marten, weasels and wolverines. Most people recognize otters both by their appearance — thick tan-and-brown fur, large whiskers, prominent noses, tubular streamlined bodies — and their smile-inducing behaviour, such as sliding water entries, group wrestling and other playful, carefree interaction. Yet, at the same time, the animals defy easy study. Individuals are hard to tell apart as they have few distinguishing markings and their necks are too thick relative to their heads for researchers to attach GPS tracking collars to them.
Consequently, large gaps remain in human understanding of otters’ social behaviour, rituals, community and family structures, uses of habitat and even their precise populations. One thing is clear: at least in parts of North America, their recovery from steep population declines is an unqualified conservation success.
IN ONTARIO, RIVER OTTERS ARE commonly seen in and near rivers, lakes, beaver ponds and in wetland complexes, though rarely in the agricultural south. Their population bottomed out sometime in the early to mid-1900s but has since rebounded, and otter numbers have been stable in the province since at least the 1970s, says Jeff Bowman, a scientist with the Ministry of Natural Resources and Forestry (MNRF).
The declines, caused by excessive trapping, water pollution and destruction of wetland habitat, were significant and proved lasting in much of the southern part of Ontario, but in central Ontario and the north, otter numbers rose after the government introduced a trapping system in the 1940s that limits the number of trappers in an area, says Bowman. By how much otter numbers rose is hard to say; MNRF does not have otter population counts and relies primarily on trapper reports for its assessment.
Across Canada, where river otters live in every province and territory except probably Prince Edward Island, research is likewise scarce. “A lot of jurisdictions don’t have other monitoring efforts [than trapper reports],” says Shannon Crowley, ecological monitoring coordinator at the John Prince Research Forest in Fort St. James, B.C., where he studies otters and other small mammals using an extensive network of camera traps.
This lack of data contrasts with the more abundant data available in the United States, where otter populations are more closely tracked after they fell steeply in the 1800s and early 1900s. The culprit: a lethal combination of unregulated trapping, extensive shoreline disruption, wetland loss and water pollution. The species’ range, which once included every U.S. state, declined by more than 25 percent. Populations were hit hard in many regions, including the northeast, south, midwest and plains states. But subsequent habitat recovery, pollution controls and water clean-up — coupled with reintroduction of otters from other regions—have brought otters back to more than 90 percent of their historic range, a recovery comparable, at least in some regions, to the revival of the bald eagle. Crowley calls the effort “hugely successful,” adding that it shows that “if you provide the right conditions and the right management,” it is possible for a species to quickly bounce back.
The recovery was helped, no doubt, by the biology and cooperative behaviour of river otters. They reach sexual maturity early, at age two, and can have a litter of one to six kits (or pups) in spring. The young leave within the first year, but they often gather in groups to hunt, play, travel and even rear their young. Two of the most common groupings are composed of males or a mother with her current year’s offspring. The latter are sometimes accompanied by another female or male, possibly related to the mother.
THESE RELATIONSHIPS, WHICH OFTEN involve companionable behaviour, are a big reason why the species appeals to Annamarie Beckel. An ecologist and novelist who lives on the Otonabee River near Lakefield, Beckel did her graduate research on otters and remains enchanted by their “fun-loving” disposition.
“There are not too many animals that can make you laugh out loud with what they do,” she says. Observing them at play, wrestling and sliding, Beckel often found herself thinking, “What in the world are they doing?” or “Why are they doing that?”
When she was studying otters, she was taught to interpret every behaviour an animal exhibited through the lens of its potential benefit to the animal, especially if it was “costly” in that it used up time and energy. In young animals, it is assumed that play trains them for hunting or escape. But adult otters wrestling does not seem to fit the potential benefit theory, says Beckel. “They may be testing each other as potential mates, but it’s still an open question.” Beckel recently wrote a novel featuring otters, called Weaving Water. In fiction, she says, she can ascribe motives scientific literature cannot address. “There, I could say I think they’re just enjoying it: that touch is pleasurable to them, grooming is pleasurable to them.”
Other scientists share Beckel’s fascination. Crowley notes that some otter behaviour defies easy explanation. During the ice-free season, he points out, the creatures seem “carefree and playful — not going from meal to meal.” Equally unusual is river otters’ defecation ritual, carried out in repeat visits to the same latrine sites on shorelines and riverbanks. Unlike sea otters or beavers, which can defecate while in water, river otters appear to always “go” on land. But doing so involves an amazing physical dance, says Reid. “They stand fairly erect [with] their tails stuck out behind them horizontal to the ground, and they stamp their feet and jump up and down as they go.”
When a group of otters is present — which is more common in summer and fall — they all participate. “It makes you laugh out loud,” says Beckel. “One goes up the bank to poop, then two or three others follow, do a little dance and then poop, right in sequence.”
According to Crowley, some latrine sites are used for decades by successive generations of otters. While the animals are not considered very territorial, they clearly use these sites to communicate with other otters as they navigate home ranges as large as several hundred square kilometres (at least in regions where lakes and wetlands are widespread) in search of food. Besides defecating and urinating at the latrine sites, they rub their bodies on the ground, marking the spots with their anal scent glands. Other otters can infer from such markings how many animals were present, their genders, reproductive status, maturity and what they ate, among other details.
The latrines provide information for researchers too. “For an animal that is other- wise hard to study, these sites give us a window on them,” says Crowley, noting that DNA technology now allows scientists to understand relationships within groups of the animals and also to more accurately estimate population size. Even so, the elusiveness of understand- ing otter behaviour persists: according to Reid, DNA in otter scat appears to degrade quickly compared to other carnivores.
WHILE RIVER OTTER POPULATIONS are healthy across Canada, some conservation concerns remain. Crowley points to the limited number of documented natal dens, an important gap in knowledge with implications for buffer protection needed to keep logging, mining and development work away from otters rearing their litters. While otters are often assumed to have their natal dens close to water — typically in bank burrows or dens built by beavers or other animals — Crowley says the small number of studies done by tracking females surgically implanted with radio transmitters shows the dens are often 200 to 300 metres from the water’s edge. In such cases, a proper buffer would need to extend from the shore to beyond the den, yet most existing buffers are much narrower.
Reid, meanwhile, stresses the need to establish buffer zones around areas of open water in winter, calling them “habitat hot spots” seldom recognized in environmental impact assessments. “It’s a big need through most of the boreal region, because these open water areas are relatively rare,” he says. Not only do otters use them to get fish, but some fish and bird species also need them.
“Getting through the winter is tough,” says Reid. Animals like river otters rely on having predictable locations where they can catch fish — and maybe find a few snapping turtles too.