Castor canadensis
THE beaver is the world's second-largest rodent [the largest is the South American capybara], weighing up to 100 pounds; however, 50 pounds is considered very large. Except for the nursing female, both sexes look exactly alike from external appearances. They breed in mid-winter and give birth 90 days later, in April or May.
Beavers do not breed until their second or third winter and average only four per litter. They are equipped with four opposing chisel-like teeth in powerful jaws that enable them to secure the bark and branches on which they live for the cold half of the year. During the summer they feed on aquatic vegetation to a large extent. To enable them to survive the north's cold winters, beavers engage in an activity which sets them apart from most other mammals. They build dams. Dams are built for several reasons, but the foremost is to create a pond in which they can build a house and store their winter food supply. With this achieved, a beaver can live out the entire winter without entering the outside world above the ice and snow. Beavers also build dams to facilitate transportation of construction material and food from the growing site to their utilization site. For them, dam construction is as natural as burying a bone is for a dog.
Dam construction is a specialized beaver art. Dams may be made of almost any material, but the average New Hampshire dam consists of a pile of brush, mostly alder, positioned with butts downstream. This brush is faced with a thick coating of mud and rocks. Constant attention makes these dams very effective in holding water. The trees and brush are hauled to the dam site by mouth, and the mud and stones are scooped up in outstretched fore paws and carried much as we carry wood for the wood box - except they swim with it. Most colonies will rebuild a dam faster and for a longer period than most people can remove it.
Beavers seldom cut evergreen trees. Their first choice is aspen or "popple," with willow and birch also considered preferred foods. Oak is often eaten as are several other species, but usually not until the better foods are gone. Summer food consists mostly of aquatic plants. Beavers seldom go over 100 yards from their pond in search for food. Those found over one-fourth mile from their pond are probably moving to a new territory, which they do on two occasions. The one- or two-year-old beaver often leave the home colony in search of a mate or new home. The entire colony may also move when their food supply is exhausted.
Henry Laramie is supervisor of game management, NewHampshire Fish and Game Department. His account isreprinted from the summer 1967 issue of Forest Notes, published by the Society for the Protection of NewHampshire Forests.
