The front feet are equipped with five strong toes which serve well as hands for holding twigs as the animal feeds on bark. The claws function well in all digging operations, and the arms suffice for holding gobs of mud against the chest as he pushes the load onto the dam or house. Occasionally, he carries mud in his arms as he walks up the house roof on hind legs.
The hind feet are large and webbed for swimming. Even the nails on the toes are flattened in keeping with the swimming needs. The nail of the second hind claw is double and the nail of the first toe fits down on a hard pad and is movable like a duck’s bill. These specialized claws are used for combing the fur and possibly for removing some of the large beetles that live in the fur. The prominent incisors, used for gnawing, grow continuously, as they do in all rodents, in order to compensate for wear. This is an especially fortunate adaptation for the beaver, who does so much gnawing. Otherwise his teeth would soon be worn to the gums. If an incisor for any reason is thrown out of line, so it has no surface to bite against and wear, it will become excessively elongated as it grows in a curve.
A flourishing beaver colony apparently consists of the parents, the young of the year, and the previous year’s offspring. It is for this reason that we often discover three sizes of beavers in a pond. Much of beaver activity involves cooperative projects where there is latitude for any amount of individual initiative. The dam or dams must be built, or raised, or kept in repair. The house, located either out in the pond, or partially or wholly on the shore, may require additional sticks, and toward autumn is plastered on the outside with wet mud as a sort of annual renovation. This “stucco” winterizes the lodge. Occasionally, it is decided that a new house is needed and that gives young and old plenty to do. Some beavers along Riley Creek live in bank burrows and build no dams or houses.
The author inspecting a beaver house at low water.
The most effective dam that has come to my attention was built at the outlet of Wonder Lake in 1960; it raised the water level of the lake over 2 feet. For many days the outlet stream was dry. The water held back in the lake amounted to well over 100 million cubic feet or over 7 billion pounds of water.
The water depth beside the lodge must be deepened if too shallow, so that the underwater entrance to the lodge is deep enough to keep from freezing over, and imprisoning the occupants. Also a certain depth of water is needed beside the lodge in which to store the brush pile that is the winter food supply. Another activity practised extensively by some colonies is the building of canals, some of which may have great length. The mud from the digging is deposited along the canal forming a raised border. These waterways are useful for general travel to food areas and for transporting branches and poles.
The favorite foods of the beaver include willow, aspen, cottonwood, and alder. Willow brush re-sprouts readily and grows rapidly, therefore maintains itself better than some of the other foods. Also it flourishes in the wet habitat created by the beaver ponds.
Where beavers create ponds with their dams, they produce a habitat for fish, ducks, muskrats, shore birds, moose and many other forms of water and shore life. In Wyoming, I have observed the dead trees, killed by flooding, used by herons for nesting, and one of the heron nests was later used by a pair of geese.
The rich, warm coat of the beaver has long been worn by both humans and beavers, but the beaver wears it best.