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

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.

Beaver 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.

Beavers 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.