We’re right on the verge of when beavers will no longer be able to smell fresh air, see the sun and obtain fresh bark. Until the temperature drops to around 16 degrees F. they continue to break through the thin ice covering their pond. Once the temperature remains in the teens or lower for several days, they no longer try to break through the ice and are sealed under it until spring, unless there’s a mid-winter thaw.
Once beavers are confined by the ice, their activities outside the lodge are minimal. Beavers leave their lodge in winter primarily for three reasons: 1) to swim out to their winter food supply pile and retrieve a branch which they bring back into the lodge to eat, 2) to defecate in the water, and 3) to mate in January or February. Other than these excursions, they spend most of their days in the dark, enduring life in a lodge that has a temperature of about 34 degrees F. (Thanks to Kay and Peter Shumway for photo op.)
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.
The lazy, hazy days of summer are dwindling, and beavers’ internal clocks are telling them it’s time to batten down the hatches and prepare for several months of life below the ice. This entails adding a significant amount of mud to the outside of their lodge. The mud freezes and creates an impenetrable barrier between them and predators such as coyotes that, thanks to ponds being frozen, will have access to beaver lodges. This mud is anchored by the addition of debarked branches and logs that have provided the beavers with meals of cambium during the summer.
A beaver can transport its own weight in material (roughly 45-60 pounds). Retrieving debarked pieces of wood in many cases involves carrying them over both land and water, using only jaws and sometimes a shoulder for support. A beaver’s short, muscular neck and its powerful lower jaw muscles make this possible. Try lifting one of the larger logs on a lodge or beaver dam sometime. Then imagine carrying it any distance in your mouth with no assistance from your hands. (This feat rivals that of a moose carrying two 25 – 30 pound antlers around for several months.) While there are recorded cases of beavers felling trees 150 feet tall and 5 feet in diameter, logs of this size are not used as building material for dams and lodges, but rather the bark and upper branches provide them with food. (Thanks to Roger and Eleanor Shepard and Sara and Warren Demont for photo op.)
Under ice-covered ponds and lakes in dark, cold water, sometime between December and March, beavers mate. Latitude and climate affects the length of the breeding season, which is shorter and later in colder, more northern locations and longer and earlier in warmer, more southerly regions. February is the peak mating season for New England beavers.
Beavers are classified as monogamous, as once a bond has formed, they remain as a pair throughout their life until one of the pair dies, at which point a new mate is found. However, this does not mean they don’t stray. In a study of beaver colony genetics, researchers discovered that more than half of the litters had been sired by two or more males. So much for monogamy.
What exactly is it like inside an active beaver lodge in winter? It’s dark, damp and around 32°F. The living chamber inside usually has a ceiling no more than two feet high with a diameter of 4 to 6 feet, depending on the number of individuals in the family. (A typical beaver family is composed of an adult male and female, 2 to 3 yearlings, and 2- 4 kits that were born in the spring.) Fresh air enters and carbon dioxide leaves through a central vent (where mud is not applied) and through small holes that remain under logs on the side of the lodge. When there isn’t much snow and the outside air falls well below zero, the temperature inside may drop to a degree or two below freezing, but if the sun is out, it warms right back up again during the day.
The dampness is due to the beavers’ repeated need to enter the water both to retrieve sticks from their nearby food supply pile and to defecate. Upon returning to the lodge, the humidity inside increases due to the water draining from the beavers’ fur. No small wonder that if a January thaw permits, beavers will exit their pond for some fresh air, food and a little bit of sunshine.
Once locked under the ice, beavers have only the food that they have had the foresight to store in their pond prior to it freezing to sustain themselves for the next four to five months. Sometime in September or October beavers start cutting down trees and limbing them. (The more northern the latitude, the earlier they begin this process.) Beavers have been found foraging over a third of a mile from their pond in the fall. At this time of year they tend to go further afield in order to find their preferred trees and shrubs – poplar, willow, alder and sugar maples. The branches are carried to the pond and hauled through the water to the lodge. When they approach the lodge the beavers dive down and push the butt end of the branches into the mud at the bottom of the pond and proceed to weave additional layers of branches into them.
Most caches are built as close to the entrance of the lodge as possible. A cache, or winter food supply pile, that feeds a colony of beavers consists of 1,500 to 2,500 pounds of edible bark, twigs and leaves. (On average, a beaver consumes 1 ½ pounds of food per day in the summer, and 2.2 pounds in the winter.) Because beavers don’t eat the wood, they must gather several tons of saplings and branches in order to have enough to survive.
If you look closely at yesterday’s close-up view of the food cache, you will see larger limbs on top of the pile. These larger logs are used to weight down the pile –they often consist of species that beavers aren’t particularly partial to, if they eat them at all. (Note proximity of food cache to the lodge, which is to the left in photo.)
The low water levels in our ponds this fall do have one benefit – visitors leave obvious signs in the exposed muddy banks. It is fairly astounding how much nocturnal and crepuscular wildlife regularly visits these spots and remains undetected by humans under normal conditions.