399 
Comparing winter and summer birds of our record for the three ~ 
sections of the state in the year 1906-07, we find that the winter birds 
_ per square mile were fewer by 32% than those of the summer time for 
central and northern Illinois (430 and 630 respectively), but that the 
southern Illinois birds were 22.6% more numerous per square mile in 
winter than in summer (836 to 682). This southward concentration of 
the birds of the winter will, of course, vary greatly according to the 
character of the season, severe fall and winter weather equalizing the 
Illinois distribution by driving the more sensitive species quite beyond 
the boundaries of the state. 
WINTER AND SUMMER BIRDS PER 
Square Mie, 1906—07 
Winter Summer 
Southern 836 682 
Central 440 650 
Northern 420 610 
State 520 644 
The complete list of the winter birds of our survey numbers fifty- 
two species, forty-two of which were in southern, twenty-nine in central, 
and thirty-one in northern Illinois, or thirty-seven in both the latter taken 
together. Northern and central Illinois were closely alike in the species 
of their winter birds, differing mainly in the fact that the horned lark 
and redpoll came down in very small numbers into the northern part 
of the state without reaching central Illinois, that another northerner, 
the Lapland longspur, was very abundant in northern Illinois but rare in 
central, and that the cardinal, most abundant in the’ south in winter, 
Was seen in central Illinois but not in northern. In southern Illinois, 
on the other hand, sixteen species were found which were not seen far- 
ther north. Some of these doubtless occurred in central and northern 
Illinois, but the fact that they were not seen there in 278 miles of travel 
but were found in southern Illinois in less than a third of that distance, 
is an indication that, if not wanting in the north, they were at any rate 
much more abundant southward. Furthermore, the numbers of winter 
birds per Square mile were virtually equal in the two northernmost sec- 
tions, 100 birds in northern Illinois corresponding to 105 in central, but 
in southern Illinois the number was virtually twice as great as that of 
the other sections united, 100 of the latter corresponding to 199 of the 
former. The following thirteen of our fifty-two winter species are 
required to make up 85 per cent. of the total number of birds seen and 
counted in the state, and these taken together averaged 445 to the square 
mile, or about two birds to every three acres, leaving seventy-five birds’ 
to the square mile for the remaining thirty-nine species, or more than 
eight acres to the bird. 
