192 
that with these exceptional cases eliminated our recorded numbers of 
gregarious birds per square mile may be accepted as fairly representa- 
tive of the actual facts for these two years. The doubtful species are 
the cowbird, the crow-blackbird, and the bobolink, to be dropped from 
the computation for the following reasons: 
The crow-blackbirds recorded, numbered 900 in 1907 and 2455 in 
1909, and we omit the species from this comparison because the excess 
was found mainly in September in two situations in a single section of 
the state—that is, in yards and in corn fields in northern Lllinois. The 
cowbird is omitted for a like reason, its numbers being 93 in 1907 and 
1845 in 1909, of which 1302 were in large flocks seen in September in 
yards and corn fields, in northern Illinois. 
The bobolink is dropped merely because of the restriction of its 
summer range to the northern part of the state, where the numbers 
seen were 743 for the two years together as compared with seven (doubt- 
less caught in migration) in the two other sections of the state. 
With these three species omitted, we have remaining 235 gregarious 
birds to the square mile in 1907 and 343 to the mile in 1909, an increase 
in the latter year of 46 per cent., which we are disposed to take as 
actual, but of the causes of which we can offer at present no explanation. 
Most ABUNDANT SPECIES, BOTH YEARS 
The list of birds recognized and counted in the summer months of 
1907 contained 85 species names and the corresponding list for 1909 
contained 117 names. Most of the species were seen in both years, the 
entire list for both numbering only 125; or if we include the species noted 
in an orchard survey of 1908, the total is 133. Many of the species of 
these lists were represented by relatively insignificant numbers, 21 of the 
species seen in 1907 and 19 of those seen in 1909 making up 85 per 
cent. of the total number of birds seen in those years. The 21 most 
abundant species of 1907 aggregated 550 to the square mile, and the 
remaining 68 species only 95 to the mile; and the 19 most abundant 
species of 1909 aggregated 842 to the mile, and the remaining 88 species 
only 148. 
The 19 most abundant birds of 1909, making up 85 per cent. of all 
the birds seen in that year, are all on the corresponding list for 1907, 
the latter differing only by the addition of two names, grasshopper 
sparrow and upland plover, not on the 1907 list. When we com- 
pare the numbers, and especially the ratios, of the different species (the 
base of the percentages being the total numbers of birds seen), we find 
a fairly good agreement for the two years, with a few somewhat striking 
differences, largely of the more gregarious species, as shown by the 
following table. 
The most marked discrepancies between the two years are in the 
percentages of the cowbird, bobolink, and dickcissel, those of the cow- 
bird in one year being about nine times those in the other, and those of 
