MAMMALS AS NEST BUILDERS 135 



than the moles, for not only do they excavate 

 burrows, but they build ' lodges ' and also erect 

 barriers or ' dams ' across rivers and streams. The 

 lodges are of two kinds, one of them, known as 

 the ' bank-lodge,' being placed quite close to the 

 subterranean burrow and forming a kind of annexe 

 thereto ; and the other, termed simply the ' lodge,' 

 being built in mid-stream. They are composed of 

 logs, branches, and brushwood, and take the form 

 of large oven-shaped mounds measuring from six 

 to eight feet in height, and, occasionally, twenty 

 feet across. A commodious compartment, some- 

 times having a diameter of as much as seven feet, 

 and a height of two or three feet, is situated within, 

 access to the same being obtained by several under- 

 groimd passages which lead therefrom and open 

 under water. The animals render their homes 

 watertight by plastering mud upon the thick and 

 strong outer walls with the aid of their fore-paws, 

 and cover the floor of the inner apartments with a 

 carpet of grasses, chips of wood, and the bark of 

 trees. 



In order to keep the water surrounding their 

 habitations at a more or less constant level, thereby 

 ensuring that the structiures are not left high and 

 dry in times of drought, the beavers sometimes 

 erect dams across the streams, which may measure 

 as much as one hundred and fifty to two hundred 

 yards in length. They are made of logs, branches, 

 grasses, roots, and mosses, held together and 

 rendered almost, if not quite, impervious to water 

 by a coating of clay. The creatures obtain the 



