154 



Order RODENTIA 



CASTOR CANADENSIS Kuhl 

 Beaver 



Description. — The beaver, fig. 87, is a large, dark brown, 

 semiaquatic mammal with a flat, paddle-shaped, scaly tail, 

 webbed hind feet, and small ears. 



Length measurements: head and body 26-31 inches (660-790 

 mm.) ; tail 91/2-1 0i4 inches (240-260 mm.) ; over-all about 

 35-41 inches (900-1,050 mm.) ; hind foot 6i/^-7 inches (165-180 

 mm.). Weight: usually 25-50 pounds; a weight of 78l4 pounds 

 is recorded for a specimen taken on the Mississippi River near 

 Me>xr, Adams County. 



The skull is massive and about 120 mm. (4^ inches) long. 

 The large, red-orange incisors are well suited for gnawing, and 

 the back cheek teeth well suited for grinding, fig. 73^. Dental 

 formula: I 1/1, C 0/0, Pm 1/1, M 3/3. 



Life History. — The beaver needs a continuous supply of 

 water and a supply of suitable food near water. For food it 

 prefers poplar, maple, birch, and willow; it may eat other kinds 

 of trees, as well as cattails and other aquatic plants. The trees 

 and branches cut by a colony of beavers and transported to their 

 dam serve not only as a means of retaining the water but also 

 as a pantry for food. 



A colony of beavers consists usually of an adult male and fe- 

 male and their offspring of the year and the previous year. Since 



Fig. 87. — Beaver. 



