teeny OU Ue BvOONCY bh U Le eek Tor N 3 
the mid-eighties (5-10 p.m.) on September 16 to a maximum of 97% at 
3 a.m. on September 17. 
Visibility dropped from eight miles at 10 p.m. to three miles at 3 a.m. 
and remained at this low until after 8 a.m. Although the prevailing norther- 
ly winds and lowered visibility affected the migrating birds, the factors of 
accompanying haze and heavy fog and a low cloud base of 400 to 800 feet 
(lasting from about 11 p.m. to 9 a.m.) were probably the most detrimental 
in bringing about such a high mortality. Moving with the southward-flow- 
ing air mass, the birds apparently lost altitude as visibility and cloud base 
level decreased. Workmen stated that dead birds were found ‘‘near the top” 
of the tower as well as at varying lower elevations; unfortunately, no one 
was on duty at the transmitting station so that the time of the tragedy 
is unknown. 
In a recent paper by Brewer and Ellis (1958) dealing with birds killed 
during a 21-month period (1955-1957) at WCIA tower near Seymour, Cham- 
paign County, Illinois, careful attention was given to sex and age composi- 
tion and fat condition of the recovered birds. Because of the delay in re- 
covering the birds considered here and the resulting partial destruction of 
most specimens by decomposition and maggots, complete data of this type 
could not be obtained. These authors (op. cit.) also present a possibly useful 
index for estimating the size of migrating flocks based on a combination of 
factors concerning a sample of birds killed at a tower at a particular time. 
It is interesting to note that during their study, Brewer and Ellis (1958) 
recovered on seven dates, 486 individuals (51 species) as compared with 
827 specimens (40 species) recovered by the authors resulting from the 
mortality of one flight.- Apparently a particular combination of adverse 
climatic conditions was the significant factor in causing mortality in both 
areas; Brewer and Ellis (op. cit.) summarize: “Kills occurred under condi- 
tions of 80-100 per cent cloud cover, a ceiling of 400-1600 feet, and ob- 
scured visibility.” 
The majority of the dead birds recovered lay immediately south and 
slightly east of the tower base and were found between 50 and 125 feet 
from the tower. There appeared to be no defined area of concentration of 
any particular species to indicate a separate flight of one or more species 
differing in time and/or altitude from the others. From the position and 
concentration of the dead birds, it appears that the majority hit the tower 
direct and the group of east-southeast guy cables near their point of 
attachment. 
The majority of species identified are those generally considered to be 
common fall migrants in Illinois (Smith and Parmalee, 1955). One of the 
most interesting aspects of the flight was the concentration of Olive-backed 
and Gray-cheeked Thrushes, the number (252) of these species representinz 
approximately 31 percent of the total number of birds recovered. Repre- 
sentatives of the Family Parulidae (Wood Warblers) were the most 
numerous, with individuals of 18 species, totaling 405 individuals, being 
identified. Of special note was the quantity of Tennessee (107) and Chest- 
nut-sided (67) Warblers; both are common migrants, although Brewer and 
Ellis (1958) recovered 39 specimens of the former species during their 
