Nature Bulletin No. 246-A November 26, 1966
Forest Preserve District of Cook County
Seymour Simon, President
Roland F. Eisenbeis, Supt. of Conservation
The beaver was the first hydraulic engineer. Back in the days when our
ancestors were still living in caves, the beaver had been building
elaborate dams across streams, digging canals, and sleeping safely in
artificial-island homes for thousands of years. This had a profound
effect on streams and stream valleys in Europe, Siberia and most of
North America, literally changing the face of the earth. Their dams held
back flood waters in wet seasons, maintained the flow of streams in
times of drought, and built up ground water supplies. The ponds above
these dams, which were occasionally more than 1000 feet long, allowed
sediment to settle out of the water and form broad meadows which
eventually were occupied by tracts of timber and, now, some of our
finest farmland. Waterfowl, fish, and a host of other living things
thrived here because of the beaver.
The white explorers of North America pushed westward seeking fur.
More than gold, timber, rich soil or any other one thing, the lure of
beaver fur attracted adventurers and was mainly responsible for the
opening up of the continent. Huge companies were formed and wars
were fought to control the trade in beaver pelts. For 250 years the
Hudson's Bay Company ruled most of Canada with an iron hand, and
some of the great American fortunes of today had their roots in this
early fur trade. Chicago had its beginning as a small fur-trading post.
skins were used as currency for a long period. At one time the
cost of a rifle was a pile of beaver skins the same height as the gun. In
1670, according to the records of the Hudson' s Bay Company, a beaver
pelt would buy a pound of tobacco, a one-pound kettle, four pounds of
shot, or two hatchets. The markings or "points" on a Hudson's Bay
blanket designate its weight and the number of beaver skins originally
required to purchase it. All because every man, both here and abroad,
aspired to own a tall hat made of beaver felt.
The beaver is the largest North American rodent, formerly ranging from
the Atlantic to the Pacific and from the Arctic Circle to the Gulf of
Mexico. Adults are 3 to 4 feet long, weighing 40 to 70 pounds. They
resemble a huge muskrat except that they have a broad flat tail -- their
distinguishing feature. This tail, considered a great delicacy by the early
trappers, is about a foot long and half as wide. It is used as a rudder or
for sculling while in the water, as a prop when the animal stands on its
hind legs to gnaw down a tree, and is smacked on the surface of the
water as a warning signal. The handlike fore feet, with 5 toes, are used
for digging and for handling branches, logs and rocks with great
dexterity. The hind feet are larger, with 5 long toes webbed for
swimming, and the second toe on each foot has a double claw used for
combing the fur. The underfur is brown in color and so thick and
velvety that the skin is kept dry even under water. The long coarse
guard hairs are usually reddish-brown.
live in colonies consisting of a pair of adults, a litter of "kits",
and the young of the previous year -- working together on the house or
"lodge", the dam, and in storing food on the bottom of the pond for
winter. They are strictly vegetarian, feeding on the bark of aspen,
poplar, willow, alder and other trees, as well as on water plants, grass
and wild fruits. One beaver eats the bark from 200 to 300 small trees
per year. One brood of 2 to 4 young, sometimes more, are born in late
spring or early summer, at which time the mother drives the 2-year-old
youngsters out of the colony.
The eager beaver is the busiest builder by a dam site.
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Update: June 2012