398 
treatment of the birds of the transition periods covering the spring and 
fall migrations. Our report on the summer residents has already been 
published*, and we have next to report on the winter residents of the 
state, so far as they were observed in a single season’s travel. 
The winter season is, of course, in strong contrast to summer in 
respect to the dominant species of birds and their numbers, and in the 
greater freedom of their movements, since they have only their own 
pleasures and welfare to seek, quite free from responsibility for a follow- 
ing generation which in-summer individualizes their interests, chains 
them to one locality, and dominates most of their activities. In winter 
their gregarious tendencies can assert themselves unchecked, and they 
move much more generally in flocks, sweeping widely from place to 
place, as the weather changes, in a free search for shelter and a com- 
paratively scanty food supply. The extremes of the state are also much 
more unlike at this time than in summer, the southern Illinois birds 
living under conditions approaching those of the perpetual summer of 
the tropics, while the northern Illinois birds pass their winter not far 
outside the edge of a frigid zone. How these differences are expressed 
in the number of species as well as the population densities of northern 
and southern Illinois respectively, will presently be shown. 
The winter dates of our Illinois bird survey extend from November 
23, 1906, to February 21, 1907, the northern Illinois observations having 
been made from November 23 to 30 and January 2 to 16, those for 
central Illinois from December 3 to 18 and January 16 to February 1, 
and those for southern Illinois from February 6 to 21. They show set- 
tled winter conditions in each section of the state except that three fall 
migrants, the Canada goose, Wilson’s snipe, and pipit, were seen in 
northern Illinois in November in very small numbers—2, 1, and 8 re- 
spectively. The distances traveled on these winter trips, the acreage 
covered by the survey, the numbers of birds identified and counted, and 
the average numbers per square mile are shown in the following table. 
ACREAGE OF SURVEY AND NUMBER OF BIRDS 
WINTER OF 1996 AND 1907 
: Miles | Acreage “ No. Numbers per 
Section traveled | covered | Fee of birds square mile 
Southern 88.9 1422.40 1 1858 836 
Central 147.6 2638.76 1.86 1815 440 
Northern 130.1 2317.21 1.63 1520 420 
State 366.6 6378.37 5193 520 
* The Numbers and Local Distribution in Summer of Illinois Land Birds of _ 
the Open Country. By Stephen A. Forbes and Alfred O. Gross. Bul. Ill. State ~ 
Nat. Hist. Surv., Vol. XIV. Art. 6, p. 187-218, Pl. 35-70. 2 
