Iowa, WI Beaver

Identification

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. 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 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.

 

Range and Habitat

Beavers are found throughout North America, except for the arctic tundra, most of peninsular Florida, and the southwestern desert areas. The species may be locally abundant wherever aquatic habitats are found.

Beaver habitat is almost anywhere there is a source of water year-round. Beavers build dams to modify the environment to their liking. Dam building is often stimulated by running water. The length or height of a dam generally depends upon what is necessary to slow the flow of water and create a pond. In areas of flat topography, the dam may not be over 36 inches (0.9 m) high but as much as 1/4 miles (0.4 km) long. In hilly or mountainous country, the dam may be 10 feet (3 m) high and only 50 feet (15 m) long. Beavers are adaptable and will use whatever materials are available to construct dams, such as fencing material, bridge planking, crossties, rocks, wire, and other metal, wood and fiber materials.

 

Fun Facts

Beavers are active for approximately 12 hours each night except on the coldest of winter nights.

Beavers communicate by vocalizations, posture, tail slapping and scent posts or mud mounds placed around the bank and dam.

They have a relatively long life span, but most do not live beyond 10 years.

The beaver is unparalleled at dam building and can build dams on fast-moving streams as well as slow-moving ones. They also build lodges and bank dens, depending on the available habitat.

 

Damage Identification

The habitat modification by beavers, caused primarily by dam building, is often beneficial to fish, furbearers, 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.

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 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 blasted out and replaced. Some bridges have been destroyed because of beaver dam-building activity.

 

Legal Status

The legal status of beavers varies from state to state. In some states the beaver is protected except during furbearer seasons; in others it is classified as a pest and may be taken year-round when causing damage. Because of its fur value, dam building, and resulting water conservation, it is generally not considered a pest until economic losses become extensive. Fur prices for beaver in some states, particularly in the Southeast, make it hardly worth the skinning and stretching. In some northern states, trapping is prohibited near lodges or bank dens to protect and perpetuate beaver colonies.

 

Damage Prevention and Control Methods

Exclusion
Fence small critical areas such as culverts, drains, or other structures. Install barriers around important trees in urban settings.

Cultural Methods and Habitat Modification

Eliminate foods, trees, and woody vegetation where feasible. Continually destroy dams and materials used to build dams. Install a Clemson beaver pond leveler, three-log drain, or other structural device to maintain a lower pond level and avoid further pond expansion.

Frightening
Shooting of individuals or dynamiting or other continued destruction of lodges, bank dens, and dams, where legal, will occasionally move young colonies out of an area.

Repellents
None are registered; however, there is some evidence that repellents may be useful.

Toxicants
None are registered.

Trapping
No. 330 Conibear¬ traps. Leghold traps No. 3 or larger (including coil-spring types with equivalent jaw spread and impact). Basket/suitcase type traps are primarily used for live trapping. Snares can be useful, particularly in dive sets and slides where legal.

Other Methods
Other methods rarely solve a beaver damage problem and may increase risks to humans and nontarget species.

 


ACKNOWLEDGEMENTS

The above information was adapted from PREVENTION AND CONTROL OF WILDLIFE DAMAGE with permission of the editors, Scott E. Hygnstrom, Robert M. Timm, and Gary E. Larson (Cooperative Extension Division, Institute of Agriculture and Natural Resources University of Nebraska-Lincoln, United States Department of Agriculture Animal and Plant Health Inspection Service, Animal Damage Control, Great Plains Agricultural Council Wildlife Committee).

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