164 THE AMERICAN BEAYEE. 



to four wide, leads up to the roots of a tree, back of 

 which are two logs. The burrow was excavated under 

 these fallen trees, which were much decayed, and the 

 entrance to it was under the roots of the tree in front 

 of them. No further description is necessary; and 

 this, with the foregoing illustrations, sufficiently pre- 

 sent the subject of burrows. The necessity for pro- 

 tecting the entrances to these burrows by a sufficient 

 depth of water in the pond to cover them, illustrates 

 still further the uses of the dam and the importance 

 of maintaining the pond at a uniform level. 



The small number of lodges found upon the largest 

 ponds, and the large number of burrows, renders 

 it probable that there are more beavers in every 

 pond than the lodges can accommodate; and yet it is 

 difficult to ascertain the truth of the matter. The 

 lodges are undoubtedly warmer in the summer than 

 the burrows, and therefore better adapted to the rear- 

 ing of their young. If this use determined the num- 

 ber, then the lodges would show the number of fami- 

 lies inhabiting the pond. Beavers without mates, or 

 who have lost their mates, would, in all probability, 

 lead solitary lives in burrows; and these, with the 

 full families in the several lodges would, most likely, 

 represent the number of beavers in each pond. At 

 all events, the trappers, whose rules are founded upon 

 experience and observation, estimate the number of 

 beavers in each pond by the number of lodges, reck- 

 oning eight to the lodge in the Rocky Mountain 

 region, and seven in that of Lake Superior. 



In the Cascade Mountains, the beavers live chiefly 

 in burrows in the banks of the streams, rarely con- 

 structing either lodges or dams. Upon this subject, 

 Dr. Newberry, in his rejwrt on the Zoology of Oregon 



