42 
SPRING Brrps In Hapitats 
The difficulty of determining the habitat preferences of a faunal 
group as sensitive to environmental conditions, as alert in readjutsment, 
and as capable of free and rapid locomotion as birds, 1s very great 
even in the comparatively stable summer season when their obligations 
to their young anchor them to their chosen breeding places; and it is 
many times multiplied when the period of their migration converts the 
semi-stagnant pool of bird life into a swirling stream whose very banks 
change and shift from day to day as the season advances. Our tabu- 
lated data of numbers per square mile in different habitats during the 
spring migration give us, therefore, little that is worthy of record. A 
few tentative generalizations may be made, however, from a comparison 
of numbers in the principal central [linois habitats in April and May, 
1907, with those of July of the same year. That the number of mourning 
doves in wheat should be 22 to the square mile in spring and 313 in 
July, and that the number of the most abundant birds per square mile 
of wheat shoud be 360 in spring and 837 in summer, can be readily 
understood as due to the food resources offered to birds in the fields 
of shocked grain. 
Of the seven areas large enough to appear in our central Illinois 
averages of the late spring, pastures and meadows were much the 
most thickly populated (1091 and 1086 to the square mile respectively), 
and stubble field were next (877 to the mile), while corn, wheat, oats, 
and plowed ground were curiously similar in their averages to the 
square mile, (312, 363, 302, and 332). These last figures perhaps ex- 
press the numbers attributable to a mere chance distribution of birds 
not yet settled for the summer season, and the large numbers for pas- 
tures and meadows may be taken as evidence of a choice of habitats 
most nearly like the original prairie of central Illinois. Their prepon- 
derance is further shown by the fact that it was true not only for birds 
in general but also for 14 of the 18 species on our most abundant list. 
Our woodland area of only 43% acres is too small for satisfactory 
inference, especially as only eight of our 18 more abundant birds were 
found there; but these were numerous enough to give us an average of 
1487 per square mile. Only three of them, however, were characteris- 
tically woodland species, and this average and also the even less depend- 
able ones of still smaller tracts of orchards, shrubbery, and yards and 
gardens had probably best be ignored. 
Tue Fatt Micration PERIOD 
Our available data of the fall migration period were obtained in 
1906 in central and southern Illinois only, in the former from August 
2 to October 26 inclusive, and in the latter from October 31 to No- 
vember 16. In central Illinois trips were made from Urbana past 
Danville to the Indiana line, August 29 to September 1, from Cham- 
