8 BULLETIN 1078, U. S. DEPARTMENT OF AGRICULTURE. 



hands and arms. One will come up from the water carrying a huge 

 armful, held tightly against its breast, and, rising on its strong hind 

 legs, balanced by the tail pressed on the ground behind it, walk in an 

 upright position to the top of the house and deposit its load. (See 

 Plate I, Frontispiece.) As the slanting sides of the house are often a 

 network of loose sticks, the strength and energy required of a beaver 

 in climbing in the erect position and carrying a heavy armful is 

 amazing. 



CONSTRUCTING DAMS. 



In building dams beavers work from the upstream side. Sticks, 

 leaves, grass, sods, and mud are laid across the stream and are added 

 to until the flow is checked and the water begins to rise. Then, as it 

 rises, sticks are pushed over the top and allowed to lie crisscross 

 on the lower slope (PI. IV, Fig. 1), bound in and securely held by 

 mud and earth added to the top and upper slope, until high and 

 strong enough to hold the water of the pond at the desired level and 

 to be impervious to leaks and withstand the pressure of floods. The 

 ends are extended as the water rises, and the final form and position 

 of the dams are often the result of long tests of strength and endur- 

 ance, experiments, failures, and changes; some of the larger dams 

 are the work of many generations of beavers, and even where the 

 builders were destroyed a century ago the dams still remain like solid 

 breastworks below the old beaver meadows. 



BUILDING HOUSES. 



Beaver houses (PL IV, Fig. 2) are sometimes started around a 

 burrow leading from deep water up through the edge of a marsh or 

 the bank of a stream or pond ; sometimes they rise from the bottom 

 of the pond in open water 5 or 6 feet deep, sticks and mud being piled 

 up until the surface is reached, when the structure is continued up- 

 ward until a living room can be inclosed above the water level. A 

 new house is very simple and not very tight, but before winter begins 

 the walls must be thick and strong, if it is to be used for living 

 quarters. Sticks, usually first peeled for food, are laid crisscross in 

 all directions and weighted down with mud, sods, plant roots, and the 

 wet material dug up from the bottom and banks of the pond. 



A well-built house is a dense and well- fortified structure with 

 walls often 2 or 3 feet thick, of heavily reinforced construction. 

 When well frozen the walls are hard and impenetrable even to the 

 bear and the wolverene, credited with being old-time enemies of 

 the beaver. A well-built house usually extends 5 or 6 feet above the 

 surface of the water and often as much below, and may be 20 or 

 30 feet wide at the water level. Anything larger is unusual, but I 

 have seen some which I estimated to be 7 feet high and 40 feet 

 wide. 



