The Biology and History of the Beaver are Tied to Its Fur and Its Dams

By Renn Tumlison,

 Beavers (Castor canadensis) are semi-aquatic mammals with webbed hind feet and a wide, scaly tail. The nostrils and ears are valvular, so they can be closed while underwater. When disturbed, beavers may dive quickly and slap the water with their tails, which can be as loud as a gunshot. Individuals may weigh over 23 kg (50 lbs). 

Hind Foot

Lumbering along in its wetland habitat, beavers often brush against cockleburs that can become entangled in their fur. To remove the nuisance, the claws of the second hind toe are split to form a grooming claw (pictured in photo at left), which can be used like a small comb. 

Beavers mate for life and live in colonies that consist of a male and female and their offspring from the present and the previous years. They feed on aquatic plants and most visibly on the inner bark, or cambium, of trees such as willows, birches, and cottonwoods. During periods of high water, such as when rivers flood, beavers will forage at the water line. The stem in the image at right was chewed when the flood waters were about seven feet deep (obviously, the beaver did not climb the tree to cut it). 

Beaver work hgh water
Chewed Pine

Occasionally, beavers also will chew the bark of pines (left image).

In Arkansas, beavers usually dig bank dens, but sometimes they build round lodges of mud and sticks. In either case, the burrow entrance typically is hidden below the water. Muskrats and otters also may use the lodges.  

Beaver Lodge 1
Beavers Felsenthal Union Co

 In the photograph at left, a pair of beavers sits on a lodge surrounded by backwater of the Ouachita River.

The sound of running water seems to stimulate the construction of dams. Because the dams create wetlands that are critical habitat for many other species of fish and wildlife, the beaver is known as a keystone species. The benefits of dams include restoration of wetlands, replacement of ground water that has been taken out by wells, decreased flood damage downstream after heavy rains, decreased erosion by letting silt settle out, and breakdown of toxins such as pesticides. Damage to a dam usually is repaired overnight, but spillways are allowed when water is getting too high after heavy rains.  

Beaver Swamp ouac co

Biodiversity also is increased by the ponds. River otter respond well to the new habitat, as well as frogs, salamanders, fishes, and a variety of birds including waterfowl. Flooding caused by beaver dams may kill trees in a small area, which conflicts with some human interests, but it also creates the habitat used by the previously mentioned species. That also can make more opportunities for hunters, fishermen, and wildlife watchers.  

Beavers were hunted historically to make clothing and hats. Hats were fashioned from felt made from the thick underfur. Hats made of beaver fur were more water resistant than ones made of other materials, because the fur was adapted to being wet and dried repeatedly. Unfortunately, the process required the use of mercury, which is a toxic substance that affects the nervous system. Hatmakers often developed mental problems, which led to use of the phrase “mad as a hatter.”

One of the largest North American rodents was the giant beaver (Castoroides ohioensis) that lived during the Pleistocene up to 10,000 years ago. It was about the size of a bear, 2.5 m (over 8 ft) long, and is estimated to have weighed 220 kg (485 lbs)!

The genus name (Castor) is a Greek word meaning beaver. Special glands called castors once were used to make a medicine called castoreum, but now they are used in the perfume and trapping industries. The beaver apparently uses them to mark its territory.

Fur and Underfur
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