Le one 
7 
numbers per square mile in orchards than in miscellaneous situations ; 
and an application of this test gives us the eight species of the follow- 
ing table, which may be taken, according to our data, as southern Illinois 
orchard-birds par excellence. 
PRINCIPAL ORCHARD BIRDS PER SQUARE MILE, SOUTHERN ILLINOIS SURVEY, 
SuMMER oF 1908. 
Orchards compared with all other situations. 
Per square mile 
Number 
of birds 
Not 
seen In orchards 
in orchards 
(774.5 acres) (G55 acres) 
PUPAE Sere ieka: </cvaievelelseves'e ele a's 431 356 32 
Field sparrow...........-- 333 275 10 
ESEVOCS IL Vialey cf ofercie)o.s\0/ejs: es\ela:s,0 190 157 12 
Mourning dove............. 93 77 26 
RGRUEIIICH Jove ics cle s:cie-c.s c's otic. 83 69 5 
“CHIDO BSS ea eee 81 69 2 
Carolina chickadee......... Fil 59 3 
Brown thrasher ........... 70 58 3 
Total per square mile |.............. 1,120 93 
This small group of species seems strongly attracted to the orchard 
as the most desirable place of residence or resort, either for food, nest- 
ing, or shelter and refuge, of all the situations covered by our survey— 
a peculiarity which distinguishes it from ‘the other species of our list 
whose occurrence in orchards is occasional and temporary, or at most 
secondary to their choice of some other situation. 
Economic Relations—Taken as a whole, these orchard birds of 
southern Illinois, occasional visitors as well as resident species, are 
not directly injurious there to the orchard or its products, except as a 
few of them may eat cherries; and nearly all of them are more or less 
beneficial because of their partially insectivorous habits, especially when 
foraging for their young. Of course no such group of bird residents 
can be expected to keep the injurious insects of their neighborhood 
down to the level of harmlessness, but they may exercise a constant 
restraining influence on insect multiplication and do their part towards 
checking incipient uprisings of species whose rate of increase is tem- 
porarily stimulated by unusually favorable conditions.* 
In CENTRAL AND NorTHERN ILLINOIS 
During the summers of 1906, 1907, and 1909, trips were made in 
northern and central Illinois similar to those above described for the 
*See a paper by the senior author on “The Regulative Action of Birds upon 
Insect Oscillations,” Bul. Ill. State Lab, Nat, Hist., Vol. I, Art. 6. 
