_ may vary Peptaderabiy in different years if the critical seasons are much 
Pate and the numbers of a species diminish so gradually as the boun- 
_ daries of its range are approached, that it is usually impossible to draw 
them distinctly. We have made as definite a residence classification of 
5 the birds of our lists for each section of the state as our data will permit, 
using not only our own observations but all available information both 
published and unpublished, ignoring, however, merely occasional occur- 
-rences and scanty numbers, since these are ecologically insignificant ; 
and we have drawn upon our statistical data to determine as accurately 
peas possible the movements and numerical relations of the different 
classes in the four annual seasons and the three sections of the state. 
2 It is an interesting fact that only 17.1 per cent. of the 41 midwinter 
_ species of our list were winter residents in southern Illinois, the remain- 
ing 82.9 per cent. being permanent residents in that region. In central’ 
Illinois, on the other hand,-permanent resident species were 64.3%, and in 
northern Illinois 57.2% of the whole number, the ratios thus dimin- 
& ishing rapidly northward. While the winter residence ratios remained 
fairly uniform (17.1, 17.9, and 19.0, south to north), the summer species 
present in winter increased i in numbers northward (0.0, 14.3, and 19.0), 
= and the migrant species were either absent, or present in only insignifi- 
cant number. 
Fe 
_ ComPaRIsoN or ResipeNcn RATIOS IN SECTIONS oF THE STATE, WINTER oF 1907 
Species : Permanent Winter Summer Migrant 
3 Northern 57.2 19.0 19.0 4.8 
, Central 64.3 17.9 14.3 3.5 
Southern 82.9 ar (ail 4 0.0 0.0 
All Birds | 
4 Northern 62.9 35.5 1.3 0.3 
Central 84.3 + 15,0 0.6 0.1 
Southern 69.4 30.6 0.0 0.0 
Natives 
Northern 61.4 37.0 1.3 0.3 
- Central 80.8 18.4 0.7 0.1 
Southern 68.9 Bilt 0.0 0.0 
a This is all, of course, what we should expect, more species of birds 
_ remaining throughout the year in the more equable southern climate, 
x 
and the number driven southward in winter increasing as we pass to 
areas of greater cold. The agreement of our statistics with this obvious 
inference tends to give us confidence in their sufficiency, although the 
validity of the exact numbers of our tables is nevertheless left in doubt. 
It may seem strange at first that species properly classed as summer 
residents throughout the state should be more largely represented in 
