An Otter Encounter

Apr 12, 2021


A strange otter encounter, not once but twice, resulted in a Curious North question for the Masked Biologist, who talks about the North American river otter in this week’s Wildlife Matters.

Today I have the pleasure of responding to an interesting inquiry that came in through Curious North here on WXPR. The listener wrote: “Twice this week I've heard really loud strident calls that sound almost but not quite like a raptor. Best described as chirping, but loud. Once near the Davenport street Wisconsin river bridge, the other by the Boyce drive bridge over the Pelican. The calls were echoing, as if under the bridge. I followed the sound with my binocular and eventually discovered River Otters! 2 each time. They seemed to enjoy the amplification and reverberation provided by the bridge. Here's my question. What are otters up to in mid-late March? What's the chirping all about? What type of den do otters use? What's their typical life cycle?“

What a great topic this is! I find river otters so interesting; they are a clever and complex creature by all accounts. Otters are Wisconsin’s largest member of the Mustelid, or weasel family. Its cousins include the tiny family namesake, the weasel (or ermine), as well as mink, fisher, martens and badgers. It used to include skunks as well, until a recent reclassification by scientists who put them in their own family group.

You could easily consider otters an aquatic or semi-aquatic mammal. They are at home in the water, moving far more cumbersomely on land. They are built to swim, with dense, smooth fur, a long muscular tail, a streamlined torpedo-shaped body and webbed feet. They eat mostly aquatic organisms, including crayfish, mussels, aquatic insects, frogs, turtles, and fish. While they are sometimes blamed for lower numbers of trout or gamefish in occupied waters, stomach content studies have shown that they eat more than twice as much rough fish as game fish, especially seeming to prefer chubs and suckers. Otters can hold their breath for up to eight minutes, which is important when trying to chase and catch an underwater meal.

Otters apparently breed in or under water, too. We don’t exactly know their peak breeding season, but it is likely in late spring or early summer. They are den animals, meaning they occupy a hole of some kind to give birth to their young. It might be an excavated burrow with an underwater entrance, or an old beaver lodge, sometimes even an old hollow log or other depression or hole. They have a fairly long gestation period, ten months or so, and give birth in dens in the winter, between January and May. Their litters are usually about four cubs, which are born blind and helpless. But by about three months old their parents are taking them out and teaching them how to swim and catch their own food. It would make sense that once they can feed themselves, the parents are able to breed again, and the cycle repeats. The young are fully grown at one year old, and are sexually mature and ready to mate at age two. Otters seem to do well staying in family groups, but eventually as they prepare to pair up and breed, they have to move off on their own, establish territory and find a mate.

Otters are true Northwoods residents, handling the cold and snow better than extreme heat. They are known for sliding in the snow on their bellies, usually because it’s easier than running on their relatively short legs but also because they find it fun. Makes sense, really, it’s a chance to swim on land as it were. They use holes in the ice to travel from one area to another and will even use holes drilled by ice fishermen. For air, they have to find trapped air pockets under the ice in areas where no open hole exists. This might be one reason that they like to occupy rivers, which tend to stay at least partly open most of the winter.

So what about the loud chirping under bridges on rivers in March? Well, I have a couple of ideas. First of all, under bridges because its fun. The acoustics are great, and who doesn’t love hearing the sound of their own singing voice? Otters are really not vocal creatures, normally. Not like some other animals, like raccoons, who never seem to stop chattering. Otters usually only communicate during breeding season, or to communicate with family members, maybe in a defensive posture. In this case, I would guess that these were last year’s babies, the one-year-old juveniles, being playful and enjoying the open water while their parents tend to their new siblings. It could also be that they were two-year-olds, getting a head start on advertising their territory or interacting with potential mates. Finally, maybe least likely, they could be new parents who are starting to take their young out for a swim and are vocalizing to scold or encourage them. March seems very early for that, especially this far north, where it seems unlikely that young would be born in early January.

Thanks for the topic! Keep the Curious North questions coming, and I will use them in future episodes.