\6 ILLINOIS NATURAL HISTORY SURVEY MANUAL 4 



This hypothetical case illustrates the type of reasoning that 

 may be employed in identifying signs. In many cases the list of 

 suspected mammals can be reduced to a few kinds but not to one 

 specific mammal. If a combination of signs is available, such as 

 homes and tracks or runways and food fragments, there is a 

 good chance for specific diagnosis. In some cases, signs can be 

 attributed to a specific animal with certainty. Indirect clues, 

 such as range, habitat, and season, are valid only if based on an 

 excellent knowledge of the animals likely to be present. 



Homes. — The homes of Illinois mammals fall into two chief 

 categories: burrows, or homes in the ground, and homes on or 

 above the ground. 



Some kinds of Illinois mammals are adaptable in habits, living 

 either in burrows or in homes above ground; a few kinds may 

 inhabit a variety of types of homes. Most species, however, 

 show a decided preference for particular types of homes. 



Burrows. — Mammals inhabiting burrows include those that 

 dig their own burrows and those that use burrows made by other 

 kinds of mammals. The size of the entrance, size and depth 

 of the nest below ground, and appearance of the burrow are 

 indicative of the kind of mammal living in a burrow. 



Burrows can be classified, according to size, as follows: 



1. Diameter less than 2 inches. — Characteristic of about a 

 dozen species of mice and voles, the shrews, and small rice rats. 



2. Diameter 2 to 4 inches. — Characteristic of ground squir- 

 rels, gophers, chipmunks, moles, and barn rats. 



3. Diameter more than 4 inches. — Used by large mammals 

 such as woodchucks, fig. 5, badgers, skunks, opossums, raccoons, 

 otters, and coyotes. 



Weasels and minks commonly take over homes of other spe- 

 cies. A small weasel may appropriate a mouse nest and a mink 

 may occupy a woodchuck den. 



The size of the burrow may indicate the size of the mammal. 

 The location of the burrow, the manner in which excess dirt is 

 deposited, or other signs at the den site may furnish additional 

 identifying marks. A large hole with a muddy slide nearby may 

 belong to an otter, a large one with feathers and rabbit remains 

 may be the den of a fox, and one with a musky odor may be 

 the home of a skunk or badger. 



Among the medium-sized burrows and soil dumps the follow- 

 ing are distinctive: 



