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Posts tagged “Castor canadensis

Beavers Mating

2-17-17-beaver-img_3766Under 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.

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A Beaver’s Winter Quarters

2-1-17-beaver-lodge-interior-img_4899What 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.

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Beaver Winter Food Supply Cache

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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.) 

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Beavers Especially Vulnerable

9-28-16-coyote-and-beaver-20160927_3275Little did I know when I wrote yesterday’s post about the silver lining of our low water levels that I would so quickly encounter another predator benefiting from the current drought. I have spent a considerable amount of time this summer watching three generations of beavers do their best to survive as their pond proceeded to diminish to the point of exposing one of their lodge entrances and confining them to an increasingly small body of water. The underwater entrances to a beaver lodge are vital to their protection, and predators are well aware of this.

Yesterday the importance of water as a protective barrier was made very clear to me when a coyote appeared on the opposite shore of the beaver pond from where I sat. It stood for several seconds exactly where the beavers leave the pond on their way to nearby woods to cut poplars and birches which they haul back to their pond to eat. A well-worn trail marks the spot. You could imagine the coyote, upon surveying the shallowness of the pond, telling itself to be patient, as better days were just around the corner.

Moments after the coyote left, the mother beaver got out of the pond precisely where the coyote had been standing and took a few steps before sniffing the ground and then the air (see insert). Being nocturnal, beavers have an acute sense of smell which they use for detecting danger, food and for communication with each other. It took mere seconds for the beaver to detect the scent of the coyote, at which point she turned and sought refuge in the dwindling amount of water remaining around her lodge.  May the heavens open up soon.

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Beaver Kits Out & About

9-20-16-beaver-kit-20160919_0902Last January or February beavers mated (in the water) and in May or June gave birth to 1 – 9 (average 2 – 4) precocial kits. Young beavers are born fully furred, their eyes are open and their incisors are visible. Within four days they are able to swim, but it’s usually a month or more before they are seen outside the lodge. Part of the reason for this is their buoyancy, which prevents them from diving down through the tunnel to get out of the lodge. By the age of two months they are able to submerge themselves and they have begun grooming the water-repelling secretions of their anal glands onto their fur, so they are fully water-repellent. They are ready for their semi-aquatic life.  Sometime between two and three months is when they are often first observed by humans — usually in late August or September you can see three generations of beavers in an active pond.

When they are three days old, kits begin to eat vegetation brought to them inside the lodge by their parents and year-old siblings. By the time they are two months old, they are weaned. The three-month-old kit pictured (measuring about a foot from head to base of tail) is able to debark a twig as deftly as its parents.

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Beavers Consuming Herbaceous Plants

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One associates Beavers with a fairly strict diet of bark and twigs. While their winter diet consists primarily of woody plants, they consume a variety of herbaceous and aquatic plants (as well as woody) during the spring, summer and fall months. Shrubs and trees make up roughly half the spring and autumn requirements, but as little as 10% of the summer diet when herbaceous plants such as sedges and aquatic plants become available.

Recent observation of a local active Beaver pond revealed that Interrupted Fern (Osmunda claytoniana), Jewelweed/Touch-Me-Not (Impatiens capensis) and grasses are high on the list of preferred foods of one Beaver family during the summer, although woody plants such as poplars (Populus spp.) and Paper Birch (Betula papyrifera) have also been consumed in fairly large quantities.   All too soon Beavers in the Northeast will be limited to the bark of branches they’ve stored under the ice. Until this time, they take advantage of the accessibility of more easily digested herbaceous plants. (Thanks to the Shepards and Demonts for photo op.)

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Beavers Seeking Herbaceous Plants

3-16-16 beavers out IMG_1252A recent light snow provided an opportunity to confirm that northern New England beavers have gained access to land and are seeing the sun for the first time in several months. They, along with any beavers living north of the 39th parallel, may well reap some benefit from the change in our climate. Further south, there is no real winter and beavers do not have to cope with a limited amount of stored food for there is usually no ice on ponds. Milder winters and early springs mean more time for Northeastern beavers to access herbaceous food and fresh bark, and less time locked under the ice.

Unbeknownst to many, a large portion of a beaver’s spring, summer, and fall diet consists of herbaceous food – grasses, sedges, ferns, fungi, berries, mushrooms, duckweed and even algae. When beavers first leave their ponds in the spring, one of the first foods they head for is skunk cabbage, as it is one of the earliest flowering plants to emerge (often when snow is still on the ground). Beavers also relish the new foliage of aspen, willow and alders. When they are accessible, the rhizomes, leaves and flowers of both yellow and white pond lilies are favorite foods. Come late fall, when lush greenery has disappeared, beavers up their intake of bark (cambium) and store a pile of branches on the bottom of the pond   close to their lodge, where they have underwater access to it all winter.

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