NATIONAL ZOOLOGICAL PARK—BAKER. 463 
stream. The dam is in this manner built up until the water rises, 
forming a pond. The upstream side of the dam is nearly vertical, 
and in the course of time becomes fairly regular, the lower or down- 
stream side being much more slopmg and remaining rough. At 
first the water percolates through the interstices of the structure 
but as the dam gets more compactly settled the water rises nearly 
to its top. 
Having completed the dam, the beavers proceed to build, on the 
edge of the pond, a house or lodge, pursuing the same method of 
construction by interlacing sticks. Within is a chamber, usually 
about 5 or 6 feet across and 18 or 20 inches high, having a firm, hard, 
level floor, made of small twigs and chips imbedded in earth, a few 
inches above water level. On this floor they place some dried grass 
or leaves. Here the beaver sleeps and rears his family. The lodge 
is entered from an inclined passageway commencing some 2 or 3 
feet below the level of the water in the pond, the purpose of the 
dam being to raise that level sufficiently to conceal the entrance and 
thus protect the animal from its enemies. 
The beavers are constantly at work repairing or altering the dam, 
sometimes cutting channels through it to lower the water, more 
frequently plastering it up and extending it. The dam now in the 
park, the third one built, has been repaired and reconstructed by 
them several times. This interesting work is done mostly at night; 
during the day the animals stay in their lodge and are not seen by 
visitors unless it be early in the morning or late in the afternoon. 
Like most nocturnal animals, the beaver does not see well in a bright 
light. 
In a wild state the beaver feeds almost entirely on the bark or 
tender wood of the aspen poplar, the willow, or other soft-wooded 
trees. As he does not hibernate, he usually stores up a supply of 
twigs of this kind just before winter, immersing them in water near 
his lodge. In captivity he becomes accustomed to more civilized 
fare and eats bread, roots, and other vegetable products, and occa- 
sionally may get a little bark. Im order to digest such refractory 
food, he has a large macerating pouch, larger indeed than his stomach, 
corresponding to the appendix of the intestine of man. 
The beaver is enabled to do his extraordinary work by means of 
extremely strong chisel-shaped incisors, or front teeth, which are 
separated from the others by a considerable interval and are actuated 
by very powerful muscles. He will bite a broomstick in two with 
ease, and fells large trees with no aid whatever, merely by gnawing 
around the entire circumference. One of these trees may be seen 
in the upper left-hand corner of plate 21. If caught in a steel 
trap, a beaver will sometimes free himself by gnawing off the limb 
that is seized. In one instance this was done three times; so that 
