426 
NUMBERS AND PER CENTS OF ALL BIRDS 
Permanent Winter Summer Migrants All 
Numbers 2034 875 936 124 3969 
Per cent. 51.2 22.1 23.6 Bal 100 
NUMBERS AND PER CENTS OF NATIVE BIRDS 
Permanent Winter Summer Migrants All 
Numbers 1961 875 936 124 3896 
Per cent. 50.3 22.5 24.0 Bee 100 
RESIDENCE CLASSIFICATION Ratios, FALL Prriop, CENTRAL AND 
SouTHERN ILLINOIS COMPARED 
SPECIES 
Permanent Winter Summer Migrants 
Central Illinois 20.6 bag 50.0 2305 
Southern Illinois 57.2 16.1 14,2 12.5 
NUMBERS OF ALL BIRDS 
Central Illinois 53.0 4.3 34.0 8.7 
Southern Illinois 51.2 22:.1 23.6 3.1 
NUMBERS OF NATIVES 
Central Illinois 29.7 6.4 50.9 13.0 
Southern Illinois 50.3 22.5 24.0 3.2 
The large ratios of permanent resident species and natwe birds in 
southern Illinois is of course attributable to the fact that many species 
of general summer distribution are driven by the cold from the northern 
sections into, but not beyond, the southern part of the state; and other 
differences are doubtless due in part to an advancement of the season 
by about six weeks when the southern Illinois observations were made. 
The southward concentration already referred to is most clearly 
shown by a tabulation of species and numbers of the fall birds of cen- 
tral Illinois which were found also in southern Illinois in fall. Such a. 
list comprised 48 native species, and the total number of birds of these 
species seen and counted in central Illinois was 3,919, and in southern 
Illinois 3.844,—equivalent to an average of 608 to the square mile for 
central and 1,392 for southern Illinois. That is, relatively late fall birds 
of southern Illinois were nearly 21% times as abundant to the unit of area 
as the somewhat earlier birds of the central Illinois fall. The greater 
abundance of birds in southern Illinois in winter than in summer re- 
ferred to on page 421 was thus already well marked in the latter part of 
the migration season. 
The stage of migration covered by these observations can be told 
by comparing the numbers of birds of definitely transient species (that 
is summer residents and migrants) on the fall lists for central and_ 
southern Illinois respectively, which were found in both sections of the — 
state. So doing, we find 11 such species in which central Illinois num- 
bers per square mile exceeded those for southern Illinois and 19 in 
