Introduction to Comprehensive List 



This Check List of the Birds of Illinois, prepared 

 by Mr. Gault, is intended for the use of local observers. 



As shown on the map, the State of Illinois includes 

 portions of the three life-zones into which the Austral 

 Region of North America is divided. a These life-zones 

 are based primarily on temperature, which is without 

 doubt a controlling factor, especially the mean tem- 

 perature of the breeding season (corresponding to the 

 growing season of plants) and of the colder months 

 (corresponding to the dormant season of vegetation), 

 the latter as influencing the southward migration of 

 birds; and the bioclimatic law of latitude, longitude 

 and altitude. 5 But temperature alone is not sufficient to 

 explain all the phenomena of geographic distribution ; 

 obviously other factors must be considered, such as 

 ecological conditions, and past geological history. 



While unquestionably the best graphic presentation 

 of the subject extant, the Biological Survey zone-map, 

 nevertheless, requires more or less modification in minor 

 details. It shows the Transition and Lower Austral 

 zones as barely touching the northern and southern 

 edges, respectively, of Illinois, more than ninety-nine 

 per cent of the area of the state being occupied by the 

 Upper Austral Zone. Obviously this is so far from 

 being correct that a division of the state into three 

 approximately equal divisions would -far better express 

 the facts. It should be borne in mind, however, that 

 in reality there are no "hard and fast lines" or sharply 

 defined boundaries between the life-zones, each blend- 

 ing gradually into the next, or when, as sometimes 

 happens locally, the transition is abrupt, the two areas 

 interdigitate ; and, therefore, that when a sharp division 

 is shown on a map the line of demarcation must be 

 considered an arbitrary one, especially when county 

 lines are followed, as has been done in the present 

 case for the convenience of observers. 



By far the greater number of birds (as well as other 

 animals and plants) occuring in Illinois have a range 



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