ables and still have a relatively complete and continu- 
ous record; however, most of the variables were present 
throughout the census period considered here and were 
probably not operating in any one direction to produce 
undue bias. 
The Habitat Variable.—From the earliest censuses, 
observers recorded a variety of data on the census 
localities, such as hour of starting and returning, char- 
acter of the weather, direction and force of the wind, 
and temperature. Not until the early 1940’s did census 
takers begin providing information on the kinds of habi- 
tat covered. This deficiency in basic data would be a 
serious deterrent to an evaluation of the trends in rap- 
tor populations were it not for the fact that central and 
northern [Illinois have relatively uniform terrain. Culti- 
vated land constitutes over 90 per cent of the habitat 
in these regions, and most of the censuses were taken 
in counties with less than 9 per cent of the land in 
woods (King & Winters 1952:22). 
In the consideration of numerical changes in raptor 
populations, emphasis is placed on data from the re- 
gions of the state which have been under heavy culti- 
vation throughout the period 1903-1955. In northern and 
central Illinois, the observer was never far from culti- 
vated farm land, and most of the birds of prey reported 
on counts were probably seen in or from this general 
kind of habitat. 
In southern Illinois, the part of the state with the 
most land in forest, birds reported were seen in a great- 
er diversity of habitat than in northern and central 
Illinois. Woodland species of raptors would be expected 
to appear more frequently in southern Illinois than in 
the other zones. 
The Locality Variable. - Census reports showed that 
raptors were not uniformly distributed throughout IIli- 
nois, table 1. Census localities in southern I[llinois 
averaged higher numbers of raptors than those in the 
central and northern zones. For the period 1949-1955, 
larger numbers of raptors (an average of 2.54 birds per 
party-hour) were reported for Grafton than for any other 
Illinois locality. The large number at Grafton was brought 
about in part by winter concentrations of bald eagles 
along the Mississippi and Illinois rivers in recent years. 
Similarly, Moline, situated on the Mississippi River in 
the north, has had large numbers of eagles and of other 
raptors in recent years. 
Through the years a given locality, in relation to 
other localities, has tended to show a consistent rank 
with regard to the density of its raptor populations. In 
central [llinois, Urbana regularly has reported higher 
raptor numbers than Springfield. Rockford consistently 
has reported the highest raptor numbers in northern 
Illinois. Variation in reported numbers from different 
localities in a relatively small geographic area is 
shown in the records of Chicago, River Forest, south- 
eastern Cook County, and Joliet, table 1. 
Though certain localities, such as Springfield and 
Urbana in central Illinois, have had fairly lone records 
of Christmas counts, no single locality has provided a 
complete record of counts from 1900 to 1955. In analyz- 
ing the general trends of hawk and owl populations, it 
Table 1.—Number of raptors per census-party-hour recorded on Christmas counts at different localities in northern, central, 
and southern Illinois, 1946-1955. 
Number of Raptors Recorded Per Census-Party-Hour 
Northern 
South- 
eastern 
Moline | Rockford | Chicago 
Cook Co. 
River 
Forest 
Joliet 
Central Southern 
Grafton | Murphys- 
boro 
