358 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
Most new beaver houses are begun where a feeding spot has been 
in use for a year or more, and such places are always numerous 
in a populous beaver colony. The water hole, or entrance, is the 
first step, then at its edges the peeled sticks left from many meals 
of bark are pushed back from the water’s edge, or left to sink in the 
open lake to form an island. A long and peaceful possession of a 
feeding ground and a convenient food supply are important factors 
in the location of a new house, but sometimes the necessity of a 
mother beaver to provide a place for a new family, or of a father 
beaver to move elsewhere to make room for his newly arrived 
children, or some accident to the previously occupied residence, act 
as building incentives at any season of open water. Old peeled sticks 
are brought and laid around the water door, new bushes are cut and 
added to the circle, even trees are felled and the limbs and sections 
of small trunks brought and laid on the walls until they are two 
or three feet high, then more sticks are laid over the narrowing top, 
and last of all, often not until cold weather begins, mud and sods 
are brought up in great armfuls from under water and piled over 
the sides and on top of the house. Each year more sticks and more 
mud are piled on, and the older and larger the house, the more 
settled and tangled and thicker its walls become, and the safer is the 
household within. Sometimes a new house will be so thin-walled 
that the nest within may be seen through the chinks at the top, for 
the top is the last closed and always the least solid part. 
But to return to the inside of the beaver house; instead of 
numerous rooms and elaborate apartments as once supposed, the 
inside consists of one room, generally two or three feet high, and 
three, four, or five feet wide, circular, oblong, or any shape or size, 
according as one beaver, a pair of beavers, a family, or sometimes 
two or more families, occupy it. If more room is needed the walls 
are hollowed out, the sticks cut off, and the earth dug back to make 
room in any desired direction, the massive walls, often two or 
three feet thick, allowing for any inside changes found necessary. 
Nine beavers, five young and four old, is the largest number I 
have ever found inhabiting one house, but others have reported 
larger families in very large houses. As the beavers all live in one 
room, it must be large enough to give sufficient air without becoming 
too warm, as it would if too small and crowded. More room, more 
ventilation, and lower temperature can always be obtained by mak- 
ing the walls thinner from within, and the beavers, with heavy 
fur coats to keep them warm in ice water, need cool houses. Even 
in solid old houses there is always some ventilation, and steam may 
sometimes be seen curling up from the peak on frosty mornings 
or frost crystals filling the cracks in the snow that covers the 
house in winter. 
