Fig. 3.—Localities from which raptors were reported on 
Christmas counts in northern, central, and southern [l]linois, 
1903-1955. 
Fig. 4.— Average numbers of raptors reported 
party-hour on some of the Christmas counts in 
variation is evident in several localities. 
er census- 
953. Local 
ney, Summit, Winnetka); De Kalb (Kingston); Du Page 
(Glen Ellyn, Hinsdale, Lisle); Jo Daviess (Warren); 
Kane (Batavia); Lake (Barrington, Beach, Lake Bluff, 
Waukegan, Zion); La Salle (Earlville, Ottawa); Lee 
(Dixon); McHenry (Marengo); Ogle (White Pines Forest 
State Park); Rock Island (Moline, Port Byron, Rock 
Island, Zuma Township); Whiteside (Morrison); Will 
(Channahon, Joliet); and Winnebago (Durand, Rockford). 
In central [llinois the census localities were: Adams 
(Quincy); Champaign (Champaign-Urbana, Rantoul); 
Douglas (Atwood, Hindsboro); Ford (Paxton); Fulton 
(Babylon, Fiatt); Iroquois (Milford); Kankakee (Kanka- 
kee); Macon (Decatur); Mason (Havana); McDonough 
(Bushnell); Mclean (Bloomington); Menard (Athens); 
Mercer (western Mercer County); Peoria (Peoria); Piatt 
(Monticello, White Heath); Sangamon (Berlin, Spring- 
field); and Vermilion (Danville). 
In southern Illinois the following census localities 
were represented: Alexander (Horseshoe Lake Conser- 
vation Area); Bond (Greenville); Calhoun (Brussels, 
Michael); Clark (Marshall); Clay (Ingraham); Cumberland 
(Greenup); Edwards (Albion); Jackson (Carbondale, 
Murphysboro); Jefferson (Waltonville); Jersey (Elsah, 
Grafton, Pere Marquette State Park); Marion (Centralia, 
Salem); Richland (Bird Haven Sanctuary); St. Clair 
(East St. Louis); Wabash (Mount Carmel); and William- 
son (Carterville, Crab Orchard National Wildlife Refuge, 
Marion). 
Statistical treatment of the Christmas census data, 
with their inherently high variability, was limited to 
simple methods. Calculations for frequency of occur- 
rence for each 5-year period in the record were made 
for each species. (One or more individuals of a species 
reported from a census locality constituted an occur- 
rence.) Computations of birds per mile, birds per ob- 
server-hour, and birds per party-hour were made for each 
of the relatively common species of raptors and for all 
species of raptors combined. The graphs for each spe- 
cies of raptor were plotted for only that region of the 
state which reported high frequency for the species. 
Variables Affecting Census Results 
Interpretation of quantitative data contained in the 
Christmas censuses is difficult because of the many 
variables involved. Stewart (1954:192) suggested that 
quantitative data be used to show general trends only. 
The major variables are those of locality, habitat, 
weather, number and competence of observers, time 
spent in the field, period of day spent in the field, 
methods of travel, and conspicuousness of birds. It 
was impossible to eliminate all of even the major vari- 
