Beavers are a threat to ponds, lakes and trees. Dams can cause flooding and damage to trees can cause the loss of valuable timber and landscape. Most state regulations do not allow relocation of Beaver due to overpopulation and destructive nature.
Description A very large, bulky rodent, with rounded head and small, rounded ears. Dark brown fur is fine and soft. Scaly tail large, black, horizontally flattened, and paddle-shaped. Large, black, webbed hindfoot has 5 toes, with inner 2 nails cleft. Eyes and ears small. Large, dark orange incisors. L 3-4' (900-1,200 mm); T 11 3/4-17 1/2" (300-440 mm); HF 6 1/8-8 1/8" (156-205 mm); Wt usually 44-60 lb (20-27 kg), but sometimes up to 86 lb (39 kg).
Similar Species Muskrats and Nutria are much smaller and have slender tails.
Breeding Mates late January-late February; 1-8 kits (usually 4 or 5) born after gestation of 4 months.
Habitat Rivers, streams, marshes, lakes, and ponds.
Range Most of Canada and U.S., except for most of Florida, much of Nevada, and s California.
Discussion Active throughout the year, the American Beaver is primarily nocturnal and most likely to be observed in the evening. Beavers living along a river generally make burrows with an underwater entrance in the riverbank; these are known as bank beavers. Those in quiet streams, lakes, and ponds usually build dams and a lodge. The lodge has one or more underwater entrances; living quarters are in a hollow near the top. Wood chips on the floor absorb excess moisture, and a vent admits fresh air. The chief construction materials in the northern parts of the American Beaver's range-poplar, aspen, willow, birch, and maple-are also the preferred foods. To fell a tree, the beaver gnaws around it, biting out chips in a deep groove. Small trees 2 to 6 inches (50-150 mm) in diameter are usually selected, though occasionally larger ones as much as 33 inches (850 mm) thick are felled; a willow 5 inches (125 mm) thick can be cut down in three minutes. The beaver trims off branches, cuts them into convenient sizes (about 1 to 2 inches/25-50 mm thick and 6 feet/1.8 m long), and carries them in its mouth to the dam site. There it either eats the bark, turning the branches in its forefeet as humans eat an ear of corn, or stores them underwater for winter use by poking the ends into the muddy bottom of the pond or stream. Dam designs vary widely: To lessen water pressure in swift streams, dams may be bowed upstream; in times of flood, temporary spillways may be constructed. Dam repair is constant; the sound of running water stimulates the beaver to repair the dam. Well adapted to its highly aquatic life, the beaver swims, using its webbed hindfeet, at speeds up to 6 mph (10 km/h). The tail serves as a rudder, and the forefeet are held close to the chest, free to hold objects against the chest or to push aside debris. When the animal is submerged, valves close off the ears and nostrils; skin flaps seal the mouth, leaving the front incisors exposed for carrying branches; and clear membranes slide over the eyes, protecting them from floating debris. A beaver can remain submerged for up to 15 minutes before surfacing for air. When the animal is swimming, usually only the head is visible, whereas with muskrats, both head and back are partially above water. The beaver combs its fur with the two split nails on its hindfoot, and waterproofs it by applying castoreum, an oily secretion from scent glands near the anus. A thick layer of fat beneath the skin provides insulation from chilly water in winter. On land, the beaver is far less at ease than when in the water, and frequently interrupts its activity to sniff the air and look for signs of danger. Beavers are believed to pair for life. Kits are born well furred, with eyes open, and weighing about 1 pound (.5 kg). They may take to the water inside their lodge within a half hour and are skillful swimmers within a week; if tired, they may rest or be ferried upon the mother's back.
