THE 



AMERICAN NATURALIST 



Vol. XLII August, 1908 No. 500 



THE MID-SUMMER BIRD LIFE OF ILLINOIS : A 

 STATISTICAL STUDY 1 



PROFESSOR S. A. FORBES 



In the course of a statistical survey of the bird popula- 

 tion of the State of Illinois, begun with a view to a better 

 knowledge of the significance of birds in the economy of 

 nature, two field observers, A. 0. Gross and H. A. Ray, 

 engaged in this work as assistants on the State Natural 

 History Survey, spent virtually a month of the summer 

 period of 1907 in each of the three principal sections of 

 the state— June in southern, July in central, and August 

 in northern, Illinois. Selecting in each section a locality 

 typical for that part of the state, they made regular 

 trips on foot in various directions and to various dis- 

 tances, traveling always thirty yards apart, and noting as 

 they went the species and numbers of all birds flushed by 

 them on a strip fifty yards in width, including likewise 

 those flying across this strip within a hundred yards to 

 their front. They kept record, also, by means of me- 

 chanical counters, of the distances traveled over each dis- 

 tinguishable kind of area, commonly marked by the crop 

 which is borne. 



The present paper is a report of a few of the more 

 general results of a study of the materials thus brought 

 together, illustrating the numbers and ecological distribu- 



1 Read before the Central Branch of the American Society of Zoologists. 

 505 



