Birds' natural migration strikes manmade dangers; Groups tracking tower deaths push for bird-friendly lights
Sandy Bivens and other birders took turns over the fall inspecting the ground around a hilltop television tower near White Bridge Road.
Each morning, one of them would pick up the birds that died flying into the WSMV-Channel 4 tower or its guy wires.
Yellow-breasted chats, palm warblers, red-eyed vireos, Tennessee warblers, yellow-billed cuckoos, ovenbirds, gold-crowned kinglets and others were among the 90 carcasses collected. Most are now in a freezer at the Warner Parks Nature Center.
The record of birds killed since 1960 has helped drive a debate about whether communications and cellular towers, which have been rapidly multiplying, should be more bird-friendly.
The FCC issued a request for comments last month on possible regulation changes that could include using lighting less likely to attract birds and tower construction techniques that limit or do away with guy wires.
The nonprofit American Bird Conservancy and the U.S. Fish and Wildlife Service have pressed for such improvements for years, saying that towers are among the significant causes of declines in certain bird populations, including migratory songbirds.
The WSMV tower-monitoring project is among the oldest of about four dozen long-term sites around the country.
In the earliest years after the WSMV tower was built, the number of dead birds regularly would climb near or into the thousands. It has remained under 100 for the last 10.
This year’s 90 birds – 21 species total – were the most found there since 1995, when 134 were picked up.
“This is one day’s worth right here,” said Bivens, holding up a clear plastic freezer bag with 28 assorted birds, eyes closed but feathers shimmering with green, yellow and reddish hues.
Bivens, the nature center’s director, spoke not with rancor, but with scientific interest.
She and others who volunteer in the Tennessee Ornithological Society effort are grateful that WSMV allows the research.
More than 20,000 birds total have been gathered there since 1960. The data, along with bird banding and annual bird counts, is shared with national researchers trying to piece together information about bird migration patterns and populations.
After a stay in the freezer, the Nashville tower-killed birds are stuffed or otherwise preserved for educational display.
WSMV joins study
The decision was made almost 50 years ago to give volunteers access each fall to the WSMV tower, and there’s a use for it, said Elden Hale, general manager of the station.
“We’re happy to participate in the study,” he said. “We don’t want any wildlife injured either. I think it’s in everyone’s interest to understand what happens and why.”
WSMV-Channel 4’s almost 1,370-foot tower on Knob Hill is an older version of the towers that increasing dot the country’s landscape.
Rather than an Eiffel Tower-style design with stretched-out legs, it’s straight, like a laddered steel beam standing on end. Wires spread out to anchor it to the ground.
The lights up and down the structure are required by the FCC, to warn pilots.
“If there’s a way to adjust the lighting that keeps aircraft safe and reduce the number of birds that accidentally hit the tower, we would definitely look at it,” Hale said.
“We’ll look at anything reasonable.”
He noted that birds die in many ways.
Smacking into building windows and flying into electrical lines are both estimated to take out more birds than towers.
Birds have to navigate all kinds of manmade structures during migration, said Albert Manville, a senior wildlife biologist with the U.S. Fish and Wildlife Service in Arlington, Va.
An estimated 4 million to 50 million birds die at towers. The range is wide since monitoring is done at so few of the tens of thousands of towers, making extrapolations dicey. And, towers vary in height, altitude and lighting, which can affect the likelihood of bird kills.
Also, scavengers including coyotes tend to slip in and make off with carcasses that never get counted.
Manville said his agency intends to make recommendations to the FCC that include requiring strobe lighting of a minimum intensity.
Strobe lights are preferable, with about a three-second pause between each flash, he said. Some research has shown different colors can make a difference, too.
One Nashvillian who wants change is frustrated by the process.
“Oh, please. That’s 45 years too late,” said Michael Bierly, a birder who has trained others in the science.
“There may be 75 percent less birds now than there were. The effect of the towers is far less than it was.
“If they get 20 to 30 birds a night now, they think it’s a huge kill.”
3,672 died one night
Bierly went to the WSMV tower the night of the second largest bird kill on record here, in 1970.
He had gone at 2 a.m. because the weather had turned bad and he knew ill would come of it.
The migrating birds, most neotropical songbirds headed as far as South America to winter, travel at night and seem to grow confused when fog and bad weather set in.
They fly lower and are attracted to lights. They will swirl around a lighted tower, especially when it’s one of the highest points on a landscape, as if afraid to return to the dark.
“Birds were flying all around the tower,” Bierly said. “Oh, the sounds. They were falling off the wires and hitting the pavement. Several hit me.”
Bierly spent all the next day with others picking up 3,672 birds, which included 64 species. The largest kill took place in 1968 when 5,535 died. On that day, 72 species were found. Kills on a single night at a tower in another state ranged more than 12,000.
Drop in deaths unknown
No one knows why the numbers have been down. Bierly attributes it to fewer migratory songbirds.
Bivens speculates that development with more tall buildings, more towers and more lights may be drawing birds elsewhere.
Adjusting regulations for towers should help, but more is needed, Bierly said.
“We need to look at everything that abnormally affects the survival of migrants,” he said.
By Anne Paine
|Wind Watch relies entirely
on User Funding