Beaver

Identification

The beaver (Castor canadensis) is the largest North American rodent. Most adults weigh from 35 to
50 pounds (15.8 to 22.5 kg), with some occasionally reaching 70 to 85 pounds (31.5 to 38.3 kg).
Individuals have been known to reach over 100 pounds (45 kg). The beaver is a stocky rodent
adapted for aquatic environments. Many of the beaver’s features enable it to remain submerged for
long periods of time. It has a valvular nose and ears, and lips that close behind the four large incisor
teeth. Each of the four feet have five digits, with the hind feet webbed between digits and a split
second claw on each hind foot. The front feet are small in comparison to the hind feet (Fig. 2). The
underfur is dense and generally gray in color, whereas the guard hair is long, coarse and ranging in
color from yellowish brown to black, with reddish brown the most common coloration. The prominent
tail is flattened dorsoventrally, scaled, and almost hairless. It is used as a prop while the beaver is
sitting upright (Fig. 3) and for a rudder when swimming. Beavers also use their tail to warn others of
danger by abruptly slapping the surface of the water.The beaver’s large front (incisor) teeth, bright
orange on the front, grow continuously throughout its life. These incisors are beveled so that they
are continuously sharpened as the beaver gnaws and chews while feeding, girdling, and cutting
trees. The only way to externally distinguish the sex of a beaver, unless the female is lactating, is to
feel for the presence of a baculum (a bone in the penis) in males and its absence in females.


Damage Identification

Damage and Damage Identification The habitat modification by beavers, caused primarily by dam
building, is often beneficial to fish, fur bearers, reptiles, amphibians, waterfowl, and shorebirds.
However, when this modification comes in conflict with human objectives, the impact of damage
may far outweigh the benefits. Most of the damage caused by beavers is a result of dam building,
bank burrowing, tree cutting, or flooding. Some southeastern states where beaver damage is
extensive have estimated the cost at $3 million to $5 million dollars annually for timber loss; crop
losses; roads, dwellings, and flooded property; and other damage. In some states, tracts of
bottom land hardwood timber up to several thousand acres (ha) in size may be lost because of
beaver. Some unusual cases observed include state highways flooded because of beaver ponds,
reservoir dams destroyed by bank den burrows collapsing, and train derailments caused by
continued flooding and burrowing. Housing developments have been threatened by beaver dam
flooding, and thousands of acres (ha) of cropland and young pine plantations have been flooded by
beaver dams. Road ditches, drain pipes, and culverts have been stopped up so badly that they had
to be dynamited out and replaced. Some bridges have been destroyed because of beaver
dam-building activity. In addition, beavers threaten human health by contaminating water supplies
with Giardia. Identifying beaver damage generally is not difficult. Signs include dams; dammed-up
culverts, bridges, or drain pipes resulting in flooded lands, timber, roads, and crops; cut-down or
girdled trees and crops; lodges and burrows in ponds, reservoir levees, and dams. In large
watersheds, it may be difficult to locate bank dens. However, the limbs, cuttings, and debris around
such areas as well as dams along tributaries usually help pinpoint the area.

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