Photo: Jake Schas.

An Animal You Otter Know

Nov 07, 2018 by Jen Zalewski
Northern river otters are common in Central Oregon - have you ever seen one? Learn more about these playful creatures below.

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Northern river otters (Lontra canadensis) are in the mustelid family, more commonly referred to as weasels. They are found throughout the United States and Canada, except in arid regions of the southwest. They are common in Oregon within areas where there is fresh water.

River otters are often active at dawn and dusk. Photo: Land Trust.
River otters are often active at dawn and dusk. Photo: Land Trust.
River otters are commonly crepuscular--most active at dawn and dusk. The diet of the river otter depends on where it lives, the season, and what’s available. Generally speaking, fish likely make up the majority of their diet. Other common aquatic snacks include aquatic insects, crayfish, and waterfowl. If you’re really interested in determining what your favorite local river otter is eating, you can likely find evidence of what they have recently consumed in their spraint.

Spraint is the technical word for river otter droppings. It is unknown how this term came about, but something as foul smelling as otter droppings deserves its own special name! Otters utilize and return to “latrines” where they poop, roll about, and sleep. Their latrines become deeply enmeshed in the smell of an otter and his or her kin and are thought to be a communication tool to tell other otters, “Hey, this place is taken and I am depleting all the food resources, so scram!”

Beware the otter latrine if you are walking your dog, as Fido is likely to find great pleasure in rolling in piles of sticky, fishy spraint left behind by the otter!

Here in Central Oregon, every otter you see is a northern river otter. If you head to the coast, however, things get a little tricky. Historically, sea otters did inhabit the Oregon coast. Sadly, the Oregon population was hunted to extinction in the early 1900s. The closest known population of sea otters is a reintroduced population near the Olympic Peninsula in Washington, with occasional sightings off the coast of Oregon. River otters use the ocean as well--to hunt and to move from one fresh water inlet to another. So if you see an otter in the ocean, don’t assume it’s a sea otter!

A Northern river otter on a Land Trust Preserve. Photo: Land Trust.
A Northern river otter on a Land Trust Preserve. Photo: Land Trust.
All river otters, including the ocean faring river otters discussed above, must have access to fresh water to bathe in. A dirty otter is a dead otter. That may sound dramatic, but let me explain. Unlike many aquatic mammals, otters do not possess a thick layer of fat to keep them warm. Instead, they rely on their fur to insulate and keep them warm. Their fur is incredibly dense and creates an insulating air pocket between water and their skin. Otters also have special glands that exude oil, which they use to groom their fur and provide additional waterproofing. Dirt, polluting chemicals, and salt from seawater break down these oils and disrupt the fur’s ability to trap warm air. This in effect leaves the otter vulnerable to hypothermia—it’s working harder to stay warm and burning quickly through its thin layer of fat. Yes, the river otter, like many wild animals, lives a day-to-day existence, often barely meeting its metabolic needs. Which might make you wonder why they appear to be playing all day…

River otters are famous for their frolicking and for entertaining human observers. So is this play, or something else? “Play” is common among mammals, especially immature mammals, and this activity is thought to be learning behavior--siblings play fighting, prowling around and “hunting” one another, conditioning themselves to go out into the big, bad world and make a living. But otters go sledding. In northern climates, otters have been observed climbing up snowy hillsides and sliding down again and again; apparently, just for the heck of it. Hard to believe they are not getting an adrenaline fix or training for the otter Olympics. In all likelihood, this type of behavior satisfies both self enjoyment pursuits or "play" and also physical conditioning.

Early autumn is the time of year when river otters settle down and get serious about raising a family. Well, female river otters do. The males generally only participate in the breeding portion of reproduction; then they are off to find the next female to pass along their genetics. In order to avoid giving birth in the middle of winter, otters in cold climates have a cool adaptation called delayed implantation. This adaptation allows the female’s egg to go into suspended animation shortly after fertilization and delay their pregnancy. So even though their total gestation is 230 days, the embryo is only developing the last 30 days, and the pups (average of 4), are conveniently born in the spring. Pups are born into and raised in holts. Holts are burrows in the bank of a stream with several entrances and exits. The female raises her young either alone or with the help of other related females.

River otters are often indicators of water quality. As a predator near the top of the aquatic food chain, they bioaccumulate toxins consumed by and stored in their prey. In conditions where water quality is very poor, these toxins kill otters or disrupt reproduction, leading to local eradication of the species. Many places in North America have lost their otter populations. Fortunately, regulations passed since the 1980s have banned many of these harmful pollutants and polluted waterways have recovered. The reintroduction of otters in these areas are often successful. Hopefully over time, river otters will reclaim all the territory they historically inhabited.