HOW BEAVERS BUILD THEIR HOUSES! 
By Vernon Battery, U. 8S. Biological Survey 
[With 6 plates] 
Beaver intelligence is neither human nor superhuman, as some 
would have us believe, but for the beavers’ needs it meets, far better 
than human intelligence could do, every emergency of beaver life 
except one. The one exception is the man-made trap which swept 
these wise and useful animals to the verge of extinction before man 
began to realize the foolish waste of his greedy methods. Ages ago 
the beavers learned to cope with their natural enemies, to outswim, 
outdive, outbuild most of them, and so to live safe and comfortable 
lives. As builders of houses, dams, reservoirs, and canals, they 
have become famous and have won admiration and respect. 
Their houses are not only homes, but fortifications, affording con- 
venient, comfortable, and sanitary living quarters, and safe retreats 
from most of their enemies. A well made and long-established 
beaver house, with thick walls of tangled logs, sticks, roots, sod, and 
mud would bafile any animal less powerful than a bear, armed with 
strong claws and teeth, or man, armed with cutting tools. Even 
the bear and the man would be so long delayed in forcing an en- 
trance that the occupants of the house would be far out of danger’s 
way, and safely hidden in some other house or secure bank burrow. 
Before a beaver house is begun a satisfactory location must be 
selected. Sometimes it is far from shore, out in water 5 or 6 feet 
deep, sometimes on the bank of a lake or stream, and often on 
a floating marsh just back from the edge of deep water, but always 
where a doorway from the bottom of the house leads down into water 
deep enough to remain open all winter under the ice. Out in the 
lake this is simple enough, and the doorway may open out in any 
direction; on the bank a long tunnel or subway must be dug from 
deep water up under the house to serve as an entrance and exit; on 
a floating marsh the beavers must swim under the sod and cut a 
hole up through to the surface, later building their house around 
and over it, perhaps the simplest and safest method of all. 
1 Reprinted by permission from Journal of Mammalogy, vol. 7, No. 1, February, 1926, 
pp. 4#1-44. 
357 
