JE jet AD FOO SOI Se O ARM b Ady AR iN 4] 
A Large Hawk Flight at East Peoria 
On the morning of 16 September 1972, we observed a migration of hawks 
along the Illinois River Valley near East Peoria, Tazewell County, Illinois. 
The day began heavily overcast and it was not until 10:30 a.m. that we 
first noticed the flight: a Red-shouldered Hawk (Buteo lineatus) flew close 
overhead. We then observed approximately 10 to 15 buteos circling higher 
overhead, partially concealed by the heavy cloud cover and the low 
visibility ceiling. 
The following half hour was spent watching an estimated 100 birds 
pass overhead, including 90 Broad-winged Hawks (Buteo platypterus), 7 
Red-tailed Hawks (Buteo jamaicensis), 3 Ospreys (Pandion haliaetus) and 
2 Cooper’s Hawks (Accipiter cooperi). At this point the wind velocity was 
moderate, flowing in a southerly direction at 11 knots, and the temperature 
was 64 degrees. 
The next half-hour was spent in search of a better vantage point for 
viewing the migration; consequently it does not reflect an accurate count, 
although 30 Broad-wings were identified. By 11:30 a.m. we had found a 
strategic location along the river valley at the top of a bordering ridge. 
Apparently this located us under the center of the flight path. The cloud 
cover had scattered and the temperature had warmed to 78. From this 
site it appeared that the birds were following the Illinois River. From 
11:30 a.m. to 12:00 noon we counted 150 Broad-winged Hawks. 
By noon the cloud cover had been almost totally dispersed by increas- 
ingly strong winds (14 knots), visibility was practically unlimited, and the 
temperature had reached 80. The winds were still from a_ southerly 
direction veering to southwesterly aloft, presumably. facilitating thermal 
soaring. From 12:00 to 12:30 p.m. yielded a count of approximately 100 
birds, including 95 Broad-winged Hawks, 1 Cooper’s Hawk, 2 Sharp-shinned 
Hawks (Accipiter striatus), 1 Osprey and 1 adult Bald Eagle (Haliaeetus 
leucocephalus). By 12:30 p.m. the number of birds we were seeing had 
dwindled to a few and the migration had apparently passed. For the two- 
hour period of observation we estimate that 380 birds were counted. 
An examination of weather conditions at that date and those days 
immediately preceding may offer relevant insight of conditions requisite 
for hawk migration. A summary of weather data received from the U.S. 
National Oceanic and Atmospheric Administration indicates that on 16 Sep- 
tember 1972 a low-pressure system was approaching the East Peoria area, 
moving down from central Canada, while a cold front was moving east- 
ward across the northern Midwest states and central Canada. Fairly heavy 
thunderstorms had occurred in these areas for several days prior to the 
16th, and the resultant heavy cloud cover had only begun to dissipate on 
the morning of the 16th. 
We wish to express our appreciation to Dr. Jean W. Graber for sug- 
gestions in the preparation of this report. 
—Brooks M. Burr 
Illinois Natural History Survey 
Urbana 61801 
—Steve D. Ogle 
David M. Current 
1600 W. Bradley 
Champaign 61820 
