Shorter days and longer nights trigger a flurry of activity for beavers. There is a lodge to be built, rebuilt, enlarged or repaired and a dam to be built, repaired or reinforced. As, or more, important than these tasks is cutting, gathering and transporting a supply of food for winter. Once the pond is frozen, the only food available to beavers is that which they have stockpiled under the ice. Thus, beavers spend many an autumn night adding to a growing pile of submerged branches close to the lodge. More thought is put into the harvesting of a winter food supply than one might imagine. Before cutting down a tree a beaver often tests its readiness by biting into the bark. If it is not in just the right condition — for instance, if there is still too much sap in the tree — they may speed up the drying of the bark by girdling it, and returning in several days to cut it down. If limbs and branches are stored underwater before the bark is ready, they will ferment and sour, making them unfit for food.
Beavers are constantly grooming and oiling their fur to waterproof it. Typically when grooming, a beaver sits upright with its tail curled under its body and extended in front of it between its two hind legs. This allows the cloaca (an opening which contains ducts for everything from evacuation to reproduction, plus oil and castoreum glands) to be exposed. The beaver uses its front feet to retrieve creamy-yellow waterproofing oil from its inverted oil glands and then rubs it carefully over all of its body. Without constant waterproofing the beaver’s fur would soon become soaking wet and the beaver would not be able to tolerate the cold water.
Although some ponds have had open water in spots all winter, many have remained frozen over until the recent warm weather started to melt the ice. The first open water often appears close to the lodge and along the dam of a beaver pond. It doesn’t take long for resident beavers to detect an opening, for it’s a ticket to fresh food! The first plant that beavers head for, if it’s growing in the area, is skunk cabbage. Being the first wildflower to push up through the snow, it’s usually available when ponds first open up. Aspen, willow and alder leaves, grasses, the rhizomes, leaves and flowers of water lilies, sedges, ferns, fungi, berries, mushrooms, duckweed and algae are eaten in the spring and summer by these large rodents we think of as strictly bark eaters. Photograph by Kay Shumway.
In March and April, beavers consume a lot of tree bark, but come summer, approximately 90 % of a beaver’s diet consists of grasses, aquatic plants, and other herbaceous vegetation. Of the woody plants that they do eat during the warmer months, aspen/poplar (in photograph) and willow are favorites. It appears that beavers use their sense of smell in order to find their tree of choice. The greater the distance from the pond, the more selective beavers are in terms of species chosen – they go as far as a tenth of a mile away and up steep slopes for aspen!