ARTICLE VI—The Numbers and Local Distribution in Summer of 
Illinois Land Birds of the Open Country. By STEPHEN A. ForBES AND 
ALFRED O. Gross. 
In 1913 the senior author of this paper published the product of 
a Statistical study of the midsummer birds of Illinois,* based on a part 
of the data collected by the junior author in the summer of 1907 by 
methods already repeatedly described, and of that paper the present 
- one is to be taken as a revision and continuation. The data of 1907 were 
derived from 7693.5 acres (almost all in farms) traversed in 428 miles 
of travel on foot, of which 41 per cent. was in northern, 26 per cent. 
in central, and 33 per cent. in southern Illinois. The fact that only 
tentative general conclusions could be drawn from a single year’s study 
was clearly recognized in the beginning, as is shown by the following state- 
ment in a first paper on the general subjecty: 
“The circumstance that the data of this paper are summarized in numerical 
tables must not be permitted to obscure the fact that they merely present a 
fixed picture of a fleeting condition; that they are to be taken only as numerical 
generalizations of the observations here recorded, and do not, in themselves, 
warrant much by way of inference beyond their immediate contents * * *. 
Definite conclusions of permanent value concerning the numbers and signifi- 
cance of the bird life of the state evidently can not be drawn until many such 
ure as these have been assembled, compared, and adjusted in their right 
relations.’ 
It was hence particularly desirable that additional data should be 
collected during at least a part of a second year in order that it could 
be seen to what extent those of the first year might have a somewhat 
general application, and in order also that by a combination of the two 
sets of data a broader basis might be had for generalizations of more 
stable value; and this was done by a substantial repetition, during the 
three summer months of 1909, of the summer program of 1907. 
_ There was a further special reason for repeating our first mid- 
“summer observations. The length of the State of Illinois from north to 
south brings its extremes into materially different climates, and neces- 
sitates its division, for comparative purposes, into northern, central, 
and southern sections; but these differ also in the time of onset of the 
* The Midsummer Bird be ae Pe eae By Stephen A. Forbes. Bul. Ill. State 
“} An Ornithological Cross-section of Illinois in Autumn. By Stephen A. Forbes. 
Bul. Ill. State Lab. Nat. Hist., Vol. VII, p. 332-333. 
