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 f Alfred Hitchcock made disaster films, "Birds
vs. Towers" might go something like this: It was a dark
and stormy night during fall migration season. Lacking visual
cues, the flock homed on the one source of hazy brightness in
the sky. Apparently mistaking lights of the communications tower
for the moon, some birds smashed head-on into the steel structure.
The rest circled the tower like a confused tornado, eventually
hitting one of the tower's supporting guy wires, colliding with
other disoriented birds or falling to the ground in exhaustion.
 Bird
scientists gathering at Cornell University last month for the
annual American Ornithologists' Union (AOU) meeting looked ahead
to fall migration time with renewed dread. Although birds have
been hitting structures in North America for at least 100 years,
there are now more tall towers than ever before especially for
cellular phone and digital television transmission with even
more on the drawing boards.
"The
more towers, the more dead birds," said Bill Evans, a consulting
ornithologist for the Cornell Laboratory of Ornithology who helped
organize the first scientific session of its kind, "Avian
Mortality at Communications Towers."
"Many
of these species face degraded habitats at both ends of their
migration flights and the thousands of towers are a new threat
along the way," said Evans, citing estimates of bird collisions
with man-made objects at 4 million per year.
Flying will
become even more hazardous in the next decade, predicted Albert
M. Manville, a biologist from the US Fish and Wildlife Service
(FWS) Office of Migratory Bird Management in Arlington, VA. He
said that television stations converting to the digital format
in the United States plan to erect more than 1,000 "megatowers,"
each at least 1,000 feet tall.
The FWS biologist
said that friends of birds can expect more catastrophes such
as the Jan. 22, 1998, incident when an estimated 10,000 Lapland
longspurs died one foggy, snowy night in western Kansas. The
television tower that killed the Neotropical migrants was "only"
420 feet high.
- The Cornell
meeting brought together, for the first time, biologists from
government and academia, environmentalists, representatives of
the Federal Communications Commission (FCC), National Association
of Broadcasters and the wireless communications industry. Participants
in the meeting, which was cosponsored by FWS, the American Bird
Conservancy and the Ornithological Council, reached no consensus
but they heard plenty of alarming facts:
- Large kills almost invariably occur when
migrating birds encounter inclement weather along frontal boundaries,
and the kills are strongly associated with lights on structures,
according to R. Todd Engstrom, a biologist at the Tall Timbers
Research Station in Tallahassee, Fla. He recommended limiting
the number of new towers with "co-location" rules that
require cooperation among applicants for antenna installations,
as well as scientific studies of light's effect on migrating
birds.
- Avian navigation systems might be disrupted
by red lights or radio signals that interfere with the birds'
ability to monitor Earth's geomagnetic field, according to biologist
Robert C. Beason of the State University of New York at Geneseo.
That may explain why birds circle to reestablish their orientation
cues and are more likely to collide with towers and guy wires,
said Beason, who also called for further studies linking light,
RF (radio frequency) signals and bird behavior.
- Voluntary cutbacks on lighting in tall buildings
are saving thousands of avian lives in downtown Toronto, according
to Michael Mesure of FLAP, the Fatal Light Awareness Program
in Erin, Ontario. When Ontario Hydro replaced spot lights with
rapidly flashing strobe lights on emissions stacks at six electrical
generation stations, bird collisions decreased dramatically,
Mesure said.
- In the United States, the FCC processes approximately
70,000 applications each year for new and co-located wireless,
mass media, international and experimental radio facilities,
according to Ava Holly Berland of the FCC's Office of General
Counsel in Washington, DC. That doesn't count the annual 120,000
applications for renewal of existing licenses. Co-location saves
construction costs and is encouraged but not required by the
agency's environmental rules, she reported.
Noting
other estimates as high as 100 million birds killed each year
in collisions of all kinds, Cornell's Evans said no one really
knows. Towers in remote locations are rarely monitored, and those
that are may not reflect the full extent of avian mortality because
predators often consume the birds before biologists arrive. (At
one tower, biologists found a flea collar, apparently shed by
a pet cat taking advantage of the avian carnage.)
"But
I know this is happening because I've heard it," said Evans,
who has eavesdropped on migrating birds for 15 years with upward-pointing
microphones and twice set up equipment at the base of a 317-foot
communications tower in north-central Nebraska. Several duck
species, including blue-winged teals, were migrating when an
obstacle suddenly loomed in the dark. "I could hear their
alarm calls, the collisions," Evans said, "the sounds
of ducks falling to the ground."
Hitchcock,
who was said to prefer birds over people, would have been appalled.
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