Family CASTORIDAE 155 



the usual number in each litter is four, there may be as mam as 

 10 beavers in a colony. As the older litter approaches the age of 

 2 years, it is driven from the colony. This forced dispersion 

 results in the continuous establishment of new colonies, >ome 

 nearby, others far removed. During this dispersion, adult 

 beavers may be killed by dogs, men, or cars. Young beavers 

 may be killed by minks or by extreme fluctuations in water level. 

 By and large, beavers have few natural enemies in Illinois. 



Some beavers live in burrows in banks of lakes or streams. 

 Many others live in lodges behind their dams. Their dams may 

 be as much as 6 feet in height and 200 feet in length and so con- 

 structed as to withstand heavy floodwaters. They are made of 

 tree branches, sticks, mud, and stones, and are plastered with 

 mud on the upstream side. Their great lodges, fig. 11, built of 

 similar material, often extend 6 feet above water and are several 

 times as wide as high. From dusk to daylight, beavers work on 

 their dams or lodges — adding branches, replacing mud, or felling 

 nearby trees. Each member of a colony except the young of the 

 year is "busy as a beaver." 



Signs. — Some of the most dramatic wildlife signs in Illinois 

 are those of the beaver. In addition to their dams and lodges, 

 beavers leave such signs as felled trees, sometimes more than a 

 foot in diameter, gnawed down for food, or the stumps of trees 

 showing the characteristic wide tooth marks, fig. 28^; great piles 

 of branches stored near the lodges for food; canals several feet 

 deep and several feet wide down which they float timber; large 

 burrows 12 to 18 inches in diameter dug in stream banks; and 

 footprints, chips, droppings, nibbled cornstalks, and a host of 

 lesser signs. Branches cut into sections several feet long with 

 bark peeled from them may indicate the presence of beavers. 



Beaver droppings are loosely packed, 1-1 ij inches in length, 

 and composed principally of wood fiber. They are light and float 

 on the surface of the water only a brief time before disinte- 

 grating. They are not deposited on stones or logs in or near 

 water, as are the droppings of muskrats. 



The print of a hind foot of the beaver, fig. 28/>. measures b 

 inches in length and 5 inches across, and it shows the web con- 

 necting the toes. The print of a front foot, fig. 28tf. roughly 

 half as long as that of a hind foot, shows long claw marks. 



Distribution. — In former times, the native beaver was abun- 

 dant in Illinois. Probably (l<ist'>r canadensis michiganensis 



