Spotting otters along the Otonabee
Many wild birds and animals evoke awe when we see them. Few, however, can make us laugh out loud. The North American river otter is one of those.
Years ago, as a graduate student in ecology and animal behaviour, I studied North American river otters (Lontra canadensis) in northern Wisconsin. I am supposed to be objective about my research subjects, but I have to confess, I am not. After all these years, I am still enchanted.
Otters are a member of the mustelid family – weasels, mink, fishers, skunks, badgers, and wolverines – but they seem to have a different, more fun-loving disposition than their more serious cousins. While we can only guess at what animals think and feel, certainly to human eyes, otters appear to enjoy life. I sometimes think of them as perpetual adolescents, complete with attitude.
Otters are known as the play champions of the animal world. Anyone who has watched them for any length of time has seen them wrestle and slide. Unlike many species in which only the youngsters play, both young otters and adults engage in wrestling, object play, and sliding.
It’s not always clear, however, how much of the sliding is for fun and how much is simply the most efficient locomotion over snow and ice. They are often observed repeating a slide – running up a slope and sliding down again – which certainly looks like play, and in California, pups have been observed sliding down sand dunes and running up and sliding down again – definitely not efficient locomotion, but an activity that looks like fun.
There are lots of theories about the functions of play – learning hunting and social skills, enhancing physical and brain development, building group cohesion – but the role of play, especially among adult animals, remains a fascinating mystery.
Historically, North American river otters were found in all major waterways of the United States and Canada. Their vast geographic range, from marine environments to high mountain lakes to desert canyons, is testament to their ability to adapt to a wide variety of aquatic habitats.
Although river otters often utilize marine habitats along both the Atlantic and Pacific coasts, they should not be confused with sea otters (Enhydra lutris), a significantly larger species that is exclusively marine and found only on the west coast from California to Alaska.
North American river otter populations in Canada are still fairly healthy, and the species continues to do relatively well locally in the Kawarthas, with the abundance of rivers, lakes, and wetlands. In many areas of their range, however, particularly in the United States, otters became extinct by the mid-1800s and early 1900s, primarily as a result of humanrelated activities such as overharvest, pollution, and urbanization.
Reintroduction programs, initiated in the late 1970s, have been extremely successful in restoring extirpated otter populations to much of their historic range. Otters have also done some recovering on their own, dispersing naturally as conditions have improved.
So for now, North American river otters are holding their own, but out of 13 otter species world-wide, all but the North American river otter are endangered, threatened, or close to it. The biggest threat to otters everywhere is loss of habitat – polluted water and the destruction and degradation of wetlands.
At the top of the food web, otters are known as a “sentinel” or “indicator” species of high quality aquatic habitats. The one constant in the wide variety of habitats they occupy is the availability of fresh, clean water and an abundance of prey.
Otters are slightly near-sighted on land, but have intraocular muscles that help them to see underwater. They also use long whiskers to detect prey in dark or murky water.
They eat primarily fish and crayfish, some frogs, clams, and aquatic insects, as well as the occasional small mammal or bird. Where otters utilize marine habitats, they also dine on lobsters, mussels, and crab.
Although anglers sometimes complain about otters going after trout, numerous studies have shown that otters do not select certain species. Otters might even be considered lazy. They prey on fish in direct proportion to their availability and in inverse proportion to their swimming ability.
Their population density in a given area depends on the abundance of prey and the quality of the habitat. Males range more widely than females, but their ranges overlap. Density locally rarely averages more than one otter per two kilometers of shoreline.
Otters generally prefer areas that are less disturbed by humans, and yet there are places where they do not avoid humanoccupied shoreline. Certainly in the Kawarthas, there are otters that make extensive use of human structures and regularly show up near houses.
Adult river otters are about 1 to 1.3 m long, with a thick, tapering tail that makes up more than a third of that length. Their weight ranges from 3.5 to 15 kg in the wild, with maximum size attained at about three to four years of age. Males are somewhat larger than females. The largest animals are found in Alaska, the smallest in eastern Canada and the Great Lakes and New England regions.
Otters have short, dense fur, usually a rich chocolate brown, but sometimes more pale, especially on the belly. Unlike marine mammals, they do not have an insulating layer of fat under the skin. Instead, they rely on their incredibly dense fur for warmth and, like other members of the weasel family, have a high metabolic rate.
That fur requires a lot of care. In addition to frequent grooming, otters rub and roll in sand, grass, and snow. These rolling sites are often found near “latrines,” places where otters leave “scat.”
Otters in a group often defecate one after the other in a sort of ritual – each sniffing the feces left by one individual, then arching the back, undulating the tail, treading both back feet, and depositing more scat. The droppings are black and tarry when fresh, but as they age, they become lighter in colour as fish scales and crayfish parts become more visible.
The droppings are often rich in musk from anal scent glands. To any otter encountering these latrines, the musk communicates information regarding group size and composition, reproductive status, and other factors that are not well understood.
Given that otters occupy so many different habitats, it’s not surprising that they display a wide range of social systems, from relatively solitary to highly social.
In Alberta and coastal Alaska, where otters have been radio-tracked, individuals associate in family groups (a female and her offspring, sometimes together with related females); males form “bachelor” groups, which are not a function of kinship or age.
In Alaska, these male groups are sometimes as large as 30 otters, which may hunt cooperatively. There are always some otters, both male and female, who remain solitary.
Similarly, research in Minnesota indicates that the majority of otters, unlike other mustelids, are neither solitary nor territorial. Otters share space and tend to be attracted to each other. Not only do males form groups, but some females form groups as well, possibly to help raise young and/or to forage cooperatively.
My own research on wild but unmarked otters on a stretch of river that remained open all winter indicates that group size
varies, even in the same location. Some days I’d see only one otter, but most often there would be two to four foraging together. They spent considerable time fishing, and also grooming each other and wrestling. Occasionally, there would be as many as six or eight animals, with one small group joining another. I never observed or heard any aggressive interactions among them and, similar to the Minnesota study, the otters seemed to be attracted to each other.
Locally, otters give birth in March or April, then mate again shortly afterward. They have a form of reproduction called delayed implantation: the fertilized eggs remain “dormant” within the female for roughly nine to ten months and then implant in the uterine wall in January or February.
A typical litter includes two to four pups that are born blind, sparsely furred, toothless, and relatively helpless. They usually don’t emerge from the natal den for at least a month, and then have to be taught how to swim and to catch prey.
If you want to search for evidence of otters along a shoreline, look for their distinctive scat, filled with fish scales and crayfish parts, as well as latrines, and tracks. A good track in snow or mud shows all five toes (canid and felid tracks show only four toes); you may even be able to see the webbing between the toes.
Tracks vary with the size of the otter, but generally, the back foot, which is somewhat larger than the front, measures about 6 cm across by 7 cm long. In the winter, their telltale slides are unmistakable – long troughs about 20-24 cm wide. Beavers and porcupines sometimes make troughs in deep snow, but otter slides are distinguished by the bounding tracks within and at both ends of the slide.
The best way to see otters is to spend time outdoors, especially at dawn or dusk, near shoreline that’s not too densely populated by humans. Canoeing or kayaking is ideal, or snowshoeing in winter.
Sometimes you hear them before you see them. The vocalizations you’re most likely to hear are soft grunts and highpitched birdlike chirps that seem to be contact calls, and an explosive nasal snort that serves as an alarm call. The snort is often given when an otter “periscopes” high in the water.
If you’re impatient with searching outdoors, visit the Peterborough Zoo. The otters there are one of the most popular exhibits. Through an underground window you can watch their underwater antics and their graceful, undulating swimming.
If you want to see more otter photos, or photos of other wildlife, check out www.donaldmcleod.com
Annamarie Beckel is a writer and naturalist living on the Otonabee River near Lakefield. Her most recent novel, Weaving Water, is about otters, healing a human heart, and finding hope for an Earth imperiled by environmental destruction. All royalties are donated to the World Wildlife Fund, the International Otter Survival Fund, and the River Otter Ecology Project.