100 
90 CENTRAL ILLINOIS 
FREQUENCY (PER CENT OF CGOUNTS) 
a 
°o 
/9 Os /9 /o /9 55 /9 oF /9 Se /9 cs /9 ee / 935 99. /9 50 
Fig. 22.— Frequency of occurrence of the rough-legged hawk in central Illinois calculated for 5-year periods beginning in 
1905 and ending in 1954. The year indicates the fasecade of the 5-year period. 
100 
.90 
80 
50L 1 Eee CENTRAL ILLINOIS 
40 
30 
.20 
NUMBER OF BIRDS 
/ / / / / / / / /9 
Pee oelack en seOue 8S. F0— °%s.. 90, 8 
Fig. 23. — Average numbers of rough-legged hawks reported per observer-hour in central [llinois, 1908-1955. 
Ly 
