A Matter of Lights and Death 
by John C. Avise and Robert L. Crawford 
Every year, large numbers of birds strike transmitting 
towers. At one Florida tower, the casualties are helping 
scientists answer questions about avian migration 
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Supported by a maze of guy wires ra- 
diating to ground points up to 800 feet 
from its base, the WCTV transmitting 
tower in northern Leon County, Flori- 
da, looms above the station. Early one 
morning in October 1979, a quick sur- 
vey of the grounds, thirty-four grassy 
acres as closely mowed as a golf fair- 
way, reveals a score of fluffy clumps — 
the remains of migrating birds that 
struck the 1,010-foot tower during the 
night. The kill appears to be a typical 
one for an autumn night with overcast 
skies and northerly winds; a strong cold 
front might have brought down ten 
times as many birds. Within an hour, 
the dead have been collected and re- 
corded: five house wrens, three savan- 
nah sparrows, three palm warblers, two 
common yellowthroats, two long-billed 
marsh wrens, two yellow-billed cuck- 
oos, one grasshopper sparrow, a wood 
thrush, a chimney swift, a yellow- 
throated warbler, a pine warbler, a 
scarlet tanager, an indigo bunting, and 
an American coot. The corpses are hur- 
ried to the nearby Tall Timbers Re- 
search Station, a biological station 
perhaps best known for its work on fire 
ecology, where they are bagged, la- 
beled, and placed in a freezer for later 
study. 
In 1955, ornithologist Herbert L. 
Stoddard, Sr., initiated the study of 
birds killed at the WCTV tower, and 
nearly every morning for the past twen- 
ty-six years, researchers have collected, 
cataloged, and preserved the casualties. 
Stoddard himself, who was a founder 
and vice-president of Tall Timbers, 
checked the tower almost daily until 
1967, when advancing age finally limit- 
ed his activities. A succession of work- 
ers (most recently, Robert Crawford) 
have carried on the survey. 
The loss of an average of 1,600 birds 
every year is regrettable, but the 
WCTV tower kills have been put to 
good use over the years. They have 
been made available for a wide range of 
scientific studies requiring large num- 
bers of specimens. Dozens of publica- 
tions have resulted, on topics ranging 
from levels of pesticide residues to ge- 
netic relationships, as revealed by pro- 
tein comparisons, to energetics and fat 
metabolism. In addition, the collection 
has provided thousands of museum ref- 
erence specimens and skeletal prepara- 
tions. The long-term survey itself 
provides a wealth of information that 
could not readily be obtained in any 
other manner and that can help answer 
questions about avian migration. 
Which species are nocturnal migrants? 
What are the relative abundances, par- 
ticularly of species that are difficult to 
separate in the field (such as the Empi- 
dotiax flycatchers)? At what time of 
year does each species migrate? Is there 
differential mortality by age or sex? The 
survey has also contributed to a grow- 
ing body of knowledge on weather con- 
ditions and other factors that influ- 
ence migration and mortality at fixed 
structures. 
At the WCTV tower, kills occur vir- 
tually every night from mid-August to 
mid-November. Moderate numbers of 
migrants are often killed under perfect- 
ly clear skies, but the toll increases 
markedly with overcast conditions, es- 
pecially when the wind is from the 
north. These conditions are often asso- 
ciated with the passage of a cold front, 
the boundary between cold and warm 
air masses. Behind the front, airflow 
from the north apparently stimulates 
large flights of migrants. The birds en- 
counter storm systems along the edge 
of the front and fly lower than they nor- 
mally do, under the overcast and within 
tower heights. In addition, birds be- 
come disoriented around tower lights 
when the moisture droplets associated 
with overcast conditions increase the 
area illuminated by refraction. For a 
passing front to produce a large kill, 
however, a pool of physiologically 
primed migrants, accumulated in the 
presence of earlier, southerly winds, is 
usually necessary. 
The slaughter at WCTV is less pro- 
tracted and more erratic in the spring 
than in the autumn. Spring migrants 
also take advantage of wind patterns to 
aid their flight, moving with the south- 
erly winds blowing out of the Gulf of 
Mexico. As is true in the fall, clouds as- 
sociated with approaching weather 
fronts increase the danger of collision 
with the tower. 
Since only a fraction of the birds that 
migrate south in the fall survive to re- 
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