I. Species Description
Beavers are the largest rodents in North America. They are primarily aquatic animals. They average 3 to 4 feet in length and range from 30 to 75 pounds in weight. They have a waterproof, rich, glossy, reddish brown or blackish brown coat. The ears are short, round, and dark brown. The hind legs are longer than the front legs, making the rear end higher than the front end while walking. A beaver's incisors are long, massive and sharp and are used chiefly for gnawing. They have a split nail on the second hind toe used for grooming. Beavers are easily identified by their large paddle-shaped tails.
Beavers are found throughout all of North America except for the northern regions of Canada, the deserts of the southern United States, Mexico, and Florida. They live in lodges, of which there are three types: those built on islands, those built on the banks of ponds, and those built on the shores of lakes. The island lodge consists of a central chamber, with its floor slightly above the water level, and with two entrances. One entrance opens up into the center of the hut floor, while the other is a more abrupt descent into the water.
Beavers confine their activities to within one-half mile of their lodge or den. They are most active at night, dusk, and dawn. Daytime activity is rare except during the breeding season, when the ice melts in springtime, and in areas with little human disturbance.
Beavers eat bark and cambium (the softer growing tissue under the bark of trees). Their favorites include willow, maple, poplar, beech, birch, alder, and aspen trees. They store woody vegetation near shore for winter food. They also eat water vegetation, buds, and roots in warm weather.
II. Sensitivity to Oil Spills
Beavers spend large amounts of time in the water and rely on their fur for insulation. If externally oiled, they could suffer eye damage or become hypothermic and die. Beavers groom frequently, placing them at risk of ingesting oil. Consumption of contaminated plants could also result in oil ingestion. Ingestion of oil can result in digestive tract bleeding and in liver and kidney damage. Breathing hydrocarbon vapors can result in nerve damage and behavioral abnormalities to all mammals. Spills may also indirectly affect habitats and food resources.
III. Sensitivity to Response Methods
The following text describes potential adverse impacts to beavers resulting from various oil spill response methods and/or provides recommendations to reduce impact when these methods are implemented. This is not intended to preclude the use of any particular methods, but rather to aid responders in balancing the need to remove oil with the possible adverse effects of removal with respect to beavers. More detail about the response methods themselves can be found in the Inland Response Tactics Manual.