415 
_ the square mile in the yards and gardens of the whole state in winter 
_ as compared with 653 to the square mile in shrubbery and 42 to the 
am -same area for the state as a whole. 
Tue Sprinc Micration Pertop * 
Tue Birps or Marcu, Aprit, AND May, 1907 
The spring birds of each section of the state are divisible into 
» permanent resident species, representatives of which remain in that 
_ section the year round; winter residents lingering for a time in the lap 
of spring; summer residents gradually arriving from the south; and 
Ss migrant species which pass beyond the section to their breeding grounds 
_ farther north. As everything is in a state of flux from the beginning 
to the end of spring, and as the currents of bird life flowing northward 
4 are strongly influenced by highly variable local and temporary condi- 
tions, those of the weather especially, the product of our survey is like 
* a moving picture rather than a stationary scene, and we can have no 
~ assurance that any feature of it will be definitely reproduced i in any other 
year. A single season’s record is, in its details, one sample only of many 
courses of events which may run through the same season of successive 
years; but even a single sample is doubtless to be preferred to none. 
The state was incompletely covered in the spring of 1907 by four 
. ase one across its northern end from Waukegan to Scales Mound 
_ (March 2 to 15); two in central Illinois, from Bloomington to Cham- 
paign (March 19 to 21) and from Danville to Warsaw and thence back 
by a more southerly route (April 19 to May 31); and one along the 
eastern border from Harvey in Cook county to Brownsville in White 
county (March 26 to April 11). The whole distance thus traveled was 
442.8 miles, and the birds were recognized and counted on areas amount- 
ing to 7858 acres, of which 1875 were in northern Illinois, 3923 in 
central, and 2060 along the eastern border. The central Illinois area 
was thus about equal to the two others taken together. The total of 7276 
birds counted and listed belonged to 117 species, 23 of which were found 
on the first or northern trip, 108 on the two central Illinois trips, and 
68 on the trips along the eastern border. Five of the northern Illinois 
species, 33 of the central section, and 21 of the eastern, contributed 85 
per cent. of the total number of birds from their respective parts of 
the state. The numbers per square mile were 341 for northern, 547 for 
central, and 859 for eastern Illinois, with 593 to the square mile as an 
average for the whole area. 
If we arrange the numbers of birds per square mile in the order 
of the successive dates of the four trips, we find them increasing rapidly 
from March 2 to April 5, but falling off in the period from April 20 
to May 29 to approximately the same number as that for March 19 to 
21. This may be taken as evidence of an increasing local density of the 
bird population as the wave of the spring migration proceeded north- 
~ 
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