Beavers As Engineers

       The beavers are the largest rodents in North America. When the white men first came to this country, beaver dams, lodges and canals were common in regions of poplar, birch and willow. Today, due to the great demand for the excellent pelts, beavers have become rare except in protected areas.

       As an engineer, the beaver ranks first among animals. He is well equipped for his work, and is a good planner. His front teeth are powerful chisels, his back feet are broad and webbed, his tail is broad and flat and scaled, and his front feet are used like human hands.

       When a beaver family decides to move, it seeks a stream with a clay or gravel bottom located close to the kind of wood needed. The stream may be but a spring rippling over tiny stones. A few weeks after the beavers have chosen it as the source of their water supply, it becomes lost in a larger body of water known as a beaver pond.

       The first step in the making of a pond is the cutting off timber into lengths that can be pushed or dragged by the beavers. These are laid lengthwise on the bottom of the stream with the larger ends pointing upstream. Over these ends is placed a mass of stones and mud to weight them down. Then another layer is added and another until a dam reaching from side to side has been laid. By working roots and twigs into the brush and building the mass so that it curves up¬¨ stream the beavers soon have a structure which resists the current and causes the water above to spread and deepen. Beaver Lake in Yellowstone Park is held by an old beaver dam 700 feet long.

       Should a break or leak occur, the animals immediately repair it by forcing new materials into the opening. With their strong hands stones weighing as much as six pounds may be fitted into the cavity and mud wedged in until the dam is once more a solid wall. There are records of beavers having located and plugged leaks in man-made dams which human engineers had failed to locate.

       Once a dam has caused a pond to form, the beaver family is ready to construct its dome-shaped lodge. Usually an upturned root or stone is used as a beginning. On this is piled mud and rocks until a solid base settles on the bottom. The mud used is taken from around the base. This leaves a ditch or moat which is most useful as the water there is deeper than elsewhere in the immediate neighborhood.

Beaver family.

       On this base is built the lodge. It is made of sticks plastered with mud cement and may be as much as 20 feet across and rise 3 to 5 feet above the water. Inside is a round room about 2 feet high and 6 feet wide. It is reached by entrances which begin in the deep water and incline upwards until they open into the room above. The walls of this room are covered with mud and on the floor is a mat of twigs. It is here the beavers spend the winter safe from wolves and other molesting enemies.

       Sometimes, beavers live in burrows by the sides of lakes or swiftly moving streams. In such cases, the burrow is above water level and under a root or clump of bushes. The entrance to it will be found in the water and sheltered by an overhanging rock or tree. Sometimes, the entrance is broad enough for a man to crawl through and leads back 10 or 20 feet before it broadens into a room. The most interesting thing about such a burrow is the method of securing air. The roof is made so thin that surface air can seep through. Should the roof cave in, the beavers cleverly mend it with a network of interlacing twigs and a covering of mud.

       When the timber supply close to a beaver pond becomes exhausted, the animals either leave the region or build canals to the more distant supplies. Frequently, hillocks or points of land lie between the trees and the lodges. These only seem to cause the beavers to show their engineering skill to the best advantage. Trees and rocks disappear. The mud is removed and packed firmly along the sides until the canals look as if man had made them with machines. If necessary, branching canals wind around the foot of hills, and should the water supply be too small to float the logs, dams are constructed across the canals until the desired depth is obtained. Other canals may be cut across the points of land, thus shortening the distances the beavers must push the materials from forest to lodge.

       Many meadows, today occupied by herds of sleek, dairy cattle, owe their beginnings to the engineering works of beavers who formerly lived in the neighborhood.  Cornell

Beavers modify landscape for others.