touched. The most troublesome scav- 
engers at WCTV, however, are great 
horned owls. In an early report, Stod- 
dard wrote: “As far as Horned Owls are 
concerned we are now reconciled to the 
fact that we will have to fight them ev- 
ery Spring and Fall migration for our 
share of the frequent kills. As we re- 
move one owl, another soon appears 
and rather quickly learns when and 
where to look for dead birds.” 
The scavenger problem at WCTV be- 
came so severe that Stoddard and Rob- 
ert A. Norris, who joined the project in 
1962, reluctantly instigated various 
means of predator control. Owls, the 
primary target, were trapped and trans- 
planted to other areas, and a few partic- 
ularly wary offenders had to be killed. 
Some of the dead owls were prepared as 
scientific skins; the plumages of others 
were presented to Indian tribes of the 
Southwest for ceremonial use. One 
horned owl, trapped and banded at 
WCTV on July 15, 1974, was released 
in a national forest more than twenty 
miles south of the tower. It was re- 
trapped at the same spot on the tower 
grounds on October 5, 1977, an unusu- 
al instance of homing by this species. 
Predator control was largely discontin- 
ued in 1966, with the result that total 
recoveries of WCTV tower kills have 
dropped dramatically. At man-made 
structures elsewhere, other scavengers, 
such as gulls, coyotes, and rats, prob- 
ably cause consistent gross underesti- 
mates of total bird mortality. In 
Tennessee, even box turtles have been 
seen eating tower-killed birds. 
In the early days, with or without 
competition from scavengers, the 
WCTV survey was hampered because 
the tower grounds effectively hid most 
of the kills. Small birds are extremely 
difficult to find in anything but the 
shortest grass, and most of the grounds 
were covered by thick weeds, with the 
remainder planted in corn, sweet pota- 
toes, and other row crops. After the 
first year, however, twenty acres under 
the tower were disked and sown with 
grass; later, the area was expanded to 
thirty-four acres. Now maintained for 
the express purpose of facilitating kill 
recovery, this grassy area requires re- 
peated use of a seven-foot, tractor- 
drawn mower for ten months of the 
year. One reason the serious threat that 
towers pose to migrants generally goes 
unrecognized is that most carcasses are 
not likely to be discovered unless the 
area is fastidiously maintained. 
Probably the single worst avian mor- 
tality reported at a communication 
tower occurred during the nights of 
September 18 and 19, 1963, when an es- 
timated 30,000 birds were killed at a 
TV tower in Eau Claire, Wisconsin. In 
1975, there were 7,800 radio and 950 
TV stations in the United States, and 
their cumulative effect is surely far 
from trivial. One estimate is that in the 
United States alone, more than one mil- 
lion birds die annually in accidental 
collisions with towers. Transmitting 
towers, however, are not the only man- 
made obstacles to avian migration. 
Lighthouses, chimneys, cooling towers, 
buildings, telephone and power lines, 
and public monuments contribute to 
the toll. A recent compilation found 
more than 1,040 references relating to 
mass avian mortality at such struc- 
tures, and these may represent only a 
minute fraction of actual incidents. The 
Washington Monument in the nation’s 
capital was the site of several reported 
kills in the late 1930s. For many years 
the Empire State Building in downtown 
New York used to kill large numbers of 
birds, attracted by a powerful fixed 
beam on top of the building and later by 
the intense glow of floodlights. Efforts 
are now made to have the floodlights 
turned off during overcast migration 
periods. On the night of September 27, 
1962, about 6,000 birds met their death 
at the ceilometer of an Air Force base in 
San Angelo, Texas. Another 2,000 
birds died on September 30, 1973, at a 
1,000-foot smokestack in Chesire, 
Ohio. The Toronto-Dominion Center 
in Canada and a downtown office com- 
plex in Atlanta, Georgia, report fre- 
quent kills. The list goes on. Incidents 
of birds killed by striking windows or 
overhead wires have been less frequent- 
ly reported, but investigators have esti- 
mated that these structures may cause 
even greater mortality. 
The reasons so many migrants col- 
lide with transmitting towers and other 
tall structures remain a partial mystery. 
One theory is that transmitting towers, 
acting like giant rods, alter the electric 
field that surrounds them and some- 
how affect birds’ navigational ability. 
This hypothesis, however, cannot be 
applied to lighthouses, ceilometers, or 
other obstacles that also act as death 
traps, and a more likely candidate for 
the most important factor in migration 
disasters appears to be the lighting con- 
dition. Bright lights are alluring to 
birds, particularly on cloudy, drizzly 
nights. In 1885, ornithologist William 
Brewster described the effect at the 
Point Lepreau Lighthouse on the Bay 
of Fundy, New Brunswick. 
As soon as the sky became overcast small 
birds began to come about the light [and] 
with the advent of fog they multiplied ten- 
fold in the course of a few minutes. For the 
next hour from 30-100 were constantly in 
sight, and from one to eight to ten dashing 
at the lantern. . . . About 20% struck so 
forcibly as to injure themselves beyond hope 
of recovery, often, however, fluttering off 
the platform and down to the ground be- 
neath. ... At the height of the melee the 
scene was interesting and impressive be- 
yond almost anything that I ever witnessed. 
Above, the inky black sky; on all sides, 
dense wreaths of fog scudding swiftly past 
and completely enveloping the sea which 
moaned dismally at the base of the cliffs be- 
low; about the top of the tower, a belt of 
light projected some 30 yards into the mist 
by the powerful reflectors; and in this belt 
swarms of birds, circling, floating, soaring, 
now advancing, next retreating, but never 
quite able, as it seemed, to throw off the 
spell of the fatal lantern. 
An increased understanding of the 
conditions favoring avian mortality has 
led to some improvements in lighting 
design. In Great Britain, kills at one 
lighthouse have been drastically re- 
duced by replacing revolving white bea- 
cons with flashing bluish lights. The 
substitution of rotating- for fixed-beam 
ceilometers in the early 1960s apparent- 
ly all but eliminated kills at these instal- 
lations. Few hard data are available as 
to whether alterations in lighting condi- 
tions at communication towers success- 
fully reduce kills. The lights on towers 
have historically been red and white, 
suggesting that experiments with dif- 
ferent wavelengths, intensities, and 
flash rates of lights may be fruitful. Any 
changes in lighting design cannot, of 
course, compromise the primary func- 
tion of the lights — safety in human air 
navigation. 
If there is a happy note on which to 
close a morbid topic, it must surely be 
the productive use made by scientists of 
the WCTV tower kills. In an age all too 
often characterized by short-term eco- 
logical studies, the WCTV study is un- 
usual for its longevity. In the years 
ahead, the unfortunate birds that col- 
lide with the tower and wind up in the 
Tall Timbers freezer will continue to 
provide valuable information about 
avian migration. 
John C. A vise is associate professor of ge- 
netics in the Department of Molecular 
and Population Genetics at the Univer- 
sity of Georgia. Coauthor Robert L. 
Crawford is a curator and ornithologist 
at Tall Timbers Research Station in 
Tallahassee, Florida. 
14 
