14 TH B.A USD BeOeN 7B Us Gey 
According to the records of the Capitol Airport Weather Bureau, Spring- 
field, there were strong, prevailing north-northeast winds of 15-20 m.p.h. 
from 6 p.m. to about 12:00 midnight. During the early hours of Sept. 13, 
winds continued from the same direction but the velocity lessened to 6-12 
m.p.h. The cloud base remained at 1,500 to 1,700 feet until midnight, then 
gradually dropping to a low of 1,200 between 5:00 and 6:00 a.m. the morning 
of Sept. 13. 
In comparing weather conditions on the two nights (Sept. 1958 and 
1963) that bird mortality occurred, certain differences noted on the night of 
Sept. 12-18, 1963, probably accounted for the smaller number of birds killed. 
On the night of Sept. 16-17, 1958, heavy fog and a low cloud base of 400 to 
800 feet prevailed, apparently causing a larger number of birds to lose 
altitude and fly below the top level of the tower. There was little or no 
fog the night of Sept. 12-13, 1963, and although conditions were generally 
hazy until 12:00 p.m., the cloud base was above 1,200 feet most of the night. 
Obscured visibility with fog, haze, and mist, and a maximum cloud base 
of 1,000 feet, appear to be the most effective combination of weather con- 
ditions forcing a low altitude flight. In the first kill on Sept., 1958, the 
tower had just been completed and was not yet energized. There was no 
transmission from it while, of course, in this last kill on Sept., 1963, the 
tower was in complete operation. In both cases, the red warning lights on 
the tower were lit. 
The engineer on duty the evening of Sept. 12-13 noted that, in spite of 
haze, the top flashing light on the tower could te seen. He also stated that 
birds were heard at about 8:30 p.m., but none was seen on the ground then 
or when he left the station building at 12:30 am. Since the rain had 
stopped and the haze began dissipating about midnight, it is reasonable 
to assume that the few birds found the next day on the gravel drive and 
parking lot had been overlooked in the dark, and that the mortality took 
place sime time between 8:00 and 12:00 p.m. on Sept. 12. 
Approximately one-fourth of the dead birds were picked up within a 
fifty yard radius of the tower in all directions; the others were found (in a 
field of standing corn) directly west and slightly southwest of the tower. 
The data suggests that the flight struck the upper 150 to 200 feet of the 
tower and guy cables near their point of attachment, some birds falling 
straight down while approximately three-fourths of them fell and/or were 
blown by the strong N-NE winds to the south-southwest. Had the flight 
been much lower, some individuals would have struck the two descending 
guy cable groupings to the north and to the east-southeast; no birds were 
found beneath these groupings. 
Species recorded from the Sept. 16-17, 1958, kill but not present in the 
Sept. 12-13, 1963, mortality count included the Pied-billed Grebe, Night- 
hawk, Eastern Kingbird, Great Crested Flycatcher, Least Flycatcher, House 
Wren, Veery, Bay-brested Warbler, Pine Warbler, Connecticut Warbler, 
Mourning Warbler, Indigo Bunting, and Swamp Sparrow. Except for the 
Veery (28 birds) and the Bay-breasted Warbler (24 birds), no more than 
two individuals were recorded for any of the other species. Both the 
Veery and Bay-breasted Warbler are fairly common migrants through 
central Illinois, and their absence at the tower on the night of Sept. 12-13 
may have been the result of either having previously passed through the. 
area or of not reaching the region as yet. The Swainson’s and Gray-cheeked 
Thrushes comprised approximately 31% of the Sept. 16-17, 1958, kill, but 
only 7% of the Sept. 12-13, 1963, birds. Again, these differences may be 
