In Beaver World

by Enos A. Mills

The Lily Lake beaver house, in which the old beaver spent the drouthy winter, was a large roughly rounded affair that measured twenty-two feet in diameter. It rose only four feet above the normal water-line. This house had been three times altered and enlarged, and once raised in height. Its mud walls were heavily reinforced with polelike sticks, which were placed at the junctures of the enlargements. The one large room was more than twelve feet in diameter. Near the centre stood a support for the upper part of the house. This support was about one and a half by two and a half feet, and was composed for the most part of sticks. But few houses have this support; commonly the room is vaulted. The room itself averaged two and a half feet high. It had four entrances.

A house commonly has two entrances, but it may have only one or as many as five. Thus the way to the outer world from the inside of the house is through one or more inclined passageways or tunnels. The upper opening of these entrances is in the floor a few inches above the water-level, and the lower opening in the bottom of the pond under about three feet of water. These extend at an angle through the solid foundation of the house, are about one foot in diameter and four to fifteen feet long, and are full of water almost to floor-level. This dark, windowless hut has no other entrance.

Most beaver houses stand in a pond, though a number are built on the shore and partly in the water, and still others on the bank a few feet away from the water. The external appearance and internal construction of the houses are in a general way the same, regardless of the situation or size. Most beaver houses appear conical. Measured on the water-line, they are commonly found to be slightly elliptical. The diameter on the water-line is from five to thirty-five feet, and the height above water is from three to seven feet.

A house may be built almost entirely of sticks, or of a few sticks with a larger proportion of mud and turf. In building, a small opening is left,—or built around and over,—which is afterwards enlarged into a room.

Houses that are built in a pond usually stand in three or four feet of water. The foundation is laid on the bottom of the pond, of the size intended for the house, and built up a solid mass to a few inches above water-level. This island-like foundation is covered with a crude hemisphere or dome-shaped house, the central portion of the foundation forming the floor of the low-vaulted room which is enclosed by the thick house-walls. In building the house the beaver provide a temporary support for the combined roof and walls by piling in the centre of the floor a two-foot mound of mud. Over this is placed a somewhat flattened tepee- or cone-shaped frame of sticks and small poles. These stand on the outer part of the foundation and lean inward with upper ends meeting against and above the temporary support. The beaver then cover this framework with two or three feet of mud, brush, and turf, and thus make the walls and the roof of the house. When the outer part of the house is completed, they dig an inclined passageway, from the bottom of the pond up through the foundation, into the irregular space left between the supporting pile of mud and the walls. And of this space they shape a room, by clawing out the temporary support and gnawing off the intruding sticks. This represents the most highly developed type of beaver house.

In most houses the temporary support is not used, but a part of the wall is carried up to completion, and against it are leaned sticks, which rest upon the edge of the remaining foundation. A finished house of this kind has a slightly elliptical outline. However, many a house is a crude haphazard pile of material in which a room has been burrowed.

The room is from one to three feet high, and from three to twenty feet across. The room is a kind of a burrow and is without either door or window. Half-buried sticks make a comparatively dry floor, despite the fact that it is only a few inches above water-level. Beaver sleep on the floor, usually with tail bent along the side after the fashion of a dozing cat, in a nest of shredded wood, which they patiently make by thinly splitting and paring pieces of wood. Just why this kind of bedding is used cannot be said, but probably because this material dries more quickly, is more comfortable and more sanitary, and harbors fewer parasites. However, a few beds are made of grass, leaves, or moss.

But little earthy matter is used in the tip-top of the house, where the minute disjointed air-holes between the interlaced poles give the room scanty ventilation.

Except in a few cases where house-walls are overgrown with willows or grass, the erosive action of wind and water rapidly thins and weakens them. Hence the house must receive frequent repairs. Each autumn it is plastered or piled all over with sticks or mud. The mud covering varies in thickness from two to six inches. The mud for this purpose is usually dredged from the bottom of the pond close to the foundation of the house. It is carried up, a double handful at a time, the beaver waddling on his hind legs as he holds it with his fore paws against his breast. A half-dozen or more beaver may be carrying mud up at once. The covering not only thickens the walls and increases the warmth of the house, but also freezes and becomes an armor of stone that is impregnable to most beaver enemies. The “mudding” of the house is a part of the natural and necessary preparation for winter. It may also be a special means of protection deliberately carried out by the beaver. The fact that an occasional thick-walled or grass-covered beaver house was not thus plastered in autumn—perhaps because it did not need it—has led a few people to affirm that beaver houses are not mud-covered in the autumn. Many years of observation show that most beaver houses do receive an autumnal plastering, and the few that do not have this attention usually have thick, well-preserved walls and do not need it.

One autumn in Montana, of twenty-seven beaver houses which I examined, twenty-one received mud covering; three of the others were thickly overgrown with willows and two were grass-grown. Only one thin-walled house that needed reinforcement did not receive it; and this one, by the way, was broken into by a bear before the winter had got fairly under way.