Otter Holes
A pond can have one to two feet of ice on top of it, yet North American River Otters somehow manage to find a way to come up through the ice. How do they do this? Careful observation reveals that the ice where otter holes are found is thinner than most of the pond’s ice. Otters rely on spring-fed open water and areas of thin ice for surfacing holes. Here they break through the ice and often drag larger fish out onto the ice to eat them.
If otters are feeding in a beaver pond and they can’t find openings in the ice for fishing, they have been known to tunnel into beaver dams for access to open water. In late winter, water levels sometime drop below the ice, leaving an air space that lets otters swim and hunt beneath the ice without the need for holes. (Look closely at opening to see the actual hole beneath the surface water that they emerge from.)
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North American River Otters Foraging For Fish
Whether or not North American River Otters made the original holes evident in Wednesday’s Mystery Photo, they were responsible for keeping them open by frequently poking their heads up through them for some air. Congratulations to Noel K. for being the first to correctly identify their surface holes. This was a tricky Mystery Photo, as there were none of the usual signs of otter activity (tracks, fish remains, etc.) on the ice surrounding the holes. This is probably because the ice was too thin to support the weight of an otter. To find the most humorous response, scroll down on Wednesday’s Mystery Photo comments until you get to Peg Emerson’s.
These semiaquatic members of the weasel family are active year-round and while they are mainly nocturnal and crepuscular during the summer, they are frequently spotted during the day in winter. If otters encounter open water, they rarely resist the urge to enter it and pursue resident fish.
Thanks to their webbed feet and streamlined body, otters are accomplished swimmers and divers. They are able to reach a depth of around five feet and remain submerged for up to four minutes as they hunt underwater. Top swimming speed is seven miles per hour. (They can achieve a speed of up to 18 miles per hour when running and sliding on snow or ice.) While fish are their mainstay, these carnivores also consume frogs, snakes, turtles, insects, birds and bird eggs and the occasional mammal (mainly muskrat). Though called “river” otters, they forage in fresh, salt and brackish waters. (Thanks to Rita and Dave Boynton for photo op.)
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Otter Brown-Out
North American River Otters are not territorial in the classic sense of marking territorial boundaries. Instead they mark prime resource areas within their territory. Often, the site is near their den or a productive food area. They visit these sites repeatedly to urinate, defecate and roll around on the ground – so much so that the surrounding vegetation is often dead or dying and is referred to as a “brown-out.”
If an otter has been eating fish, its scat is often just a pile of fish scales. However, if it has been dining on crayfish and it is fresh, the scat can be tubular. No matter what form otter scat takes, a tell-tale sign (in addition to fish scales and/or crayfish exoskeletons) is the presence of clear, white or yellow mucus (scat-jellies). It is not always deposited, but occasionally you do find it. The origin of this mucus is not known – most likely it’s from the otter’s intestinal tract or its anal glands. Research shows that the presence of mucous deposits in some otter species indicates reduced prey availability or reproductive state. (Photo: Tubular otter scat is circled in red. Mucus is on right side of photo. Thanks to David Putnam and Natalie Starr for yesterday’s and today’s photo op.)
Reasons why Mystery Photo was not
Black Bear: Scat consists primarily of crayfish remains.
Beaver: Beavers defecate only in water, and individual pellets consist of tiny woody fragments resembling sawdust.
Raccoon: Raccoons have latrines where multiple scat is deposited, similar to otters. However, only otters deposit mucus.
River Otter Tails
From their nose to the tip of their tail, North American River Otters measure three to four feet long. Their tail makes up anywhere from a third to nearly a half of their length. A River Otter’s tail is very thick at its base, packed with muscles, flexible, and tapers to a point. It is used to steer when an otter is swimming slowly, propel the otter when it is swimming at high speed and to help the otter balance when it stands upright on its hind legs. River Otters, known for their powerful swimming, can reach speeds of six to seven miles per hour with the help of this appendage.
When loping through the snow, River Otters often hold their tails up off the surface of the snow, but not always. Occasionally drag marks can be seen. In the accompanying photograph, an otter had leapt up an incline, and in so doing left an imprint of its impressive tail in the snow.
(Thanks to Alfred Balch for photo op, and Joan Waltermire for her sharp eyes.)
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North American River Otters Sliding
There is no denying that North American River Otters know how to travel and have fun in winter. Whether on a flat surface such as a frozen pond or river, field, or down slopes, otters take advantage of the snow, bounding then dropping to their belly and sliding, saving precious energy. Most slides are relatively short, around 10 feet long and 6-10 inches wide, though they can be as long as 25 feet long on slippery ice. At the beginning and end of a slide there are tracks (from where they push off with their hind feet, and cease sliding and begin bounding again), creating a dot-dash pattern. Sometimes a downhill slide is used repeatedly and when it is, bobsledders have nothing over otters, as water from the otters’ coats creates an icy and very slippery slide.
For those of you who would like to view an excellent video of an otter sliding, go to https://www.youtube.com/watch?v=iBB0OLOkvIU .
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River Otter Brown-out
River Otters have latrines on land where they come to defecate, urinate and roll around, all in the same area. This area is used over and over and is referred to as roll or brown-out. The latter name is derived from the fact that much of the vegetation dies as a result of the urine and acid build-up. Most otter scat (also referred to as spraint) disintegrates fast and consists of piles of fish scales, with little form. However, if you come upon a recently-visited brown-out, or if the otter has consumed prey other than fish, such as crayfish, tubular scat can be present (see photo insert). Look for River Otter brown-outs on narrow strips of land that stick out into ponds, or a strip of land between two bodies of water. (Thanks to Squam Lakes Natural Science Center for rolling otter photo op.)
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Young Otters Just Beginning to Explore Outside Their Den
Between February and April, female North American River Otters give birth to an average of two or three young inside their dens, which tend to be near water, usually in an excavated cavity under tree roots, logs or thickets. Occasionally they have been known to give birth in abandoned beaver and muskrat lodges as well as woodchuck burrows. The mother doesn’t allow her young to exit their den until they are three or four months old, which, for the oldest litters, is in May. At this point, after their waterproof adult coats have grown in, she begins to teach them how to swim (surprisingly, this skill is not innate). The mother continues to be very protective and secretive, hiding and shielding the young (even from their father) until they are about six month old. Thus, glimpses of young otters are not likely to be had until late summer, and only then if you’re lucky. (Photo: adult river otter. Thanks to Heidi Marcotte and Tom Wetmore for photo op.)
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