The Beaver is Indeed Busy

The beaver has long been a symbol of industriousness. They are part of a healthy water ecosystem. They have a destructive side as well. A member of the rodent family, a fully grown beaver weighs 40-70 pounds and typically lives for 20 years. They are semi-aquatic with a large lung capacity. The modern beaver, Castor Canadensis, can reach 3-4 feet in length. Beavers have a disproportionately large skull and teeth which makes it possible for them to gnaw wood.

The beaver cuts through a tree trunk with his front teeth. He will drag the trunk to a specific spot in a moving river or stream and engineer the construction of his family domicile, the beaver lodge. The beaver lodge contributes to the health of the surrounding area by limiting run-off, reducing erosion, improving soil quality, and attracting other wildlife. It also provides a year-round home for the beaver and his brood.

Beavers do not rest during the winter months, they are active all year long. They store food in their lodge to get them through the cold months. They eat aquatic vegetation, leaves, twigs, and bark from aspen, willow, cottonwood, and alder trees. However, if their preferred diet is not available, they will adapt and eat whatever plant life is available.

Beavers cut down timber throughout the year, but late autumn and early spring are their busiest seasons. They are known to drag fallen trees from up to 600 feet from the water's edge. The typical trunk diameter of a harvested tree is 3-4 inches. The closer the tree is to the shore line, the larger the trunk can be.

The steadfastness of the beaver's attention to task is less admirable if the trees he is cutting down are on your property. Researchers note that fewer trees come down during the cold season if there are adequate numbers of thick, fleshy rhizomes in the water for the beaver to harvest and eat. Two species mentioned are the yellow water lily (Nuphar variegatum Nymphaea) and the American white water lily (Nymphaea odorata). The rhizomes are the stored nutrients of the plant and remain edible throughout the year.

Beavers like moving water with a stable depth and a near flat gradient. Beavers usually like marshes, ponds, and lakes. They build their lodges in open water or near the shore. The beavers look for locations that offer protection from the wind and waves. The opening to the lodge will be below the water line.

Beavers are social animals. They form colonies as long as there is a suitable food supply. The head of the colony is a monogamous pair of adult beavers. If a mate dies, the widowed beaver will take a new mate. The beaver pair produce a litter of four to six kits each year. The colony will include the offspring from the previous year and the offspring of the current year. The younger generations will either build their own lodge or take over an abandoned lodge that meets their needs. When the beaver offspring are two years old, they will move on and start their own colony.

The beaver is willing to live along side humans as long as the food, water, and construction materials are accessible. Neighboring humans should be alert for lodges that will block culverts and drainage pipes. Beavers do have predators: human traps, coyotes, lynx, otters, wolverines, wolves, and bears. Beavers are generally considered beneficial and laws have been passed to protect them in public areas.

Beavers are trapped for their pelts which are valued in the fur trade industry. Pelts are graded by size and quality (holes, rips, tears, or bald spots). Prices range from $22.50 for an extra-small craft grade pelt up to $275 for a large fashion grade pelt with tail and feet.

Beavers have a long history as a species. They are in the same family, but not descendants of the Giant Beaver that lived in the marshes created by the receding glaciers up until 11,000 years ago. Giant Beavers are labeled Castoroides Ohioensis. These very large rodents reached 7 feet in length and weighed in at 275 pounds. There are open questions about whether or not Ohioensis felled trees or built dams and lodges. Their fossilized remains are found throughout much of the United States and research is ongoing to establish the details of their palaeoenvironment. They are part of the greater mystery of the demise of the megafauna that included the mammoth and mastodon. The conversation continues about whether their disappearance was due to over-hunting by early people, disease, or both.

The threats to the modern American beaver are easier to see. Better understanding of their value to the environment and a willingness to get along have eased the stress on the declining beaver populations.

Sources
Allen, A. W. 1982. Habitat suitability index models: Beaver. U.S. Dept.
Int., Fish Wildl. Servo FWS/OBS-82/10.30. 20 pp., http://www.nwrc.usgs.gov/wdb/pub/hsi/hsi-030.pdf
Fleming Outdoors, http://www.flemingoutdoors.com/beaver-trapping-tips.html
Chichester Inc. http://www.chichesterinc.com/Beaver.htm
University of Michigan Museum of Zoology, http://animaldiversity.ummz.umich.edu/site/accounts/information/Castor_canadensis.html
Palaeoecology of a Northeast Indiana Wetland Harboring Remains of the Pleistocene Giant Beaver (Castoroides Ohioensis), 2001, Proceedings of the Indiana Academy of Science 110:151-166