6 ILLINOIS NATURAL HISTORY SURVEY MANUAL 4 



Geographical Distribution. — Each species of mammal is able 

 to exist only in certain types of habitat and under certain cli- 

 matic conditions. The area in which a species exists is called its 

 range or distribution pattern. The range for each species may 

 change as the habitat or other conditions change. 



Enough collecting has been done to provide a knowledge of 

 the approximate range of each species of Illinois mammal, but 

 for many species the details of distribution are not well under- 

 stood. A knowledge of the range of the species is valuable in 

 giving clues concerning climatic or habitat conditions which 

 control its distribution. 



The study of the geographic distribution of mammals is ex- 

 tremely interesting, and amateur collectors have a real oppor- 

 tunity to make worth-while contributions to this study. The 

 value of their contributions, however, depends on the care and 

 accuracy with which they collect, preserve, and label their 

 material. Instructions for the collector are given in this book, 

 and a general knowledge of the ranges of North American 

 mammals can be gleaned from such standard mammalogy books 

 as A Field Guide to the Mammals by Burt (1952) or The 

 Mammal Guide by Palmer (1954). The collector can check 

 his records against the maps and accounts of distribution in 

 these books as well as in the following pages to see if he has 

 records of interest. 



Species State-Wide in Occurrence. — Of the 59 species of 

 wild mammals in Illinois, 36 occur throughout the state or in 

 localities scattered throughout the state. These 36 species in- 

 clude some whose ranges center in Illinois and others whose 

 ranges center to the north, south, east, or west of this state. 

 Species such as the cottontail and the house mouse are abundant 

 and of state-wide distribution in Illinois; others such as the 

 white-tailed deer and the beaver are also state-wide in distribu- 

 tion but are comparatively rare and sporadic in their occurrence. 



The distribution pattern and abundance of the various spe- 

 cies of mammals reflect the occurrence, extent, and quality of 

 habitats suitable for their existence. For example, chipmunks 

 occur in many localities in Illinois but are confined to wooded, 

 ungrazed hills and ravines. Moles are generally distributed in 

 Illinois but, as they require well-drained soils, few of them are 

 found in the marsh and bog areas of the extreme northern part 

 of the state. 



