Tower Kill: Our Burgeoning Network of Towers for Mobile Phones, Pagers, and Digital Television Kills Millions of Migratory Birds a Year-And Prevention May Be as Simple as Changing a Lightbulb
Eaton, Joe, Earth Island Journal
It's a rainy night in Georgia, and across the state line in northern Florida. Under a low ceiling on this October evening in 1955, thousands of neotropical migrant songbirds--warblers, thrushes, vireos, tanagers, buntings--are moving south. They would be navigating by the stars if the skies were clear, but with conditions like this they fall back on their ability to sense the earth's magnetic field. Normally their flight plans would take them across the Gulf of Mexico, to the Yucatan and beyond. Tonight, though, the final destination for many of the birds lies just ahead: the 669-foot-high broadcasting tower of station WCTV, on the Tall Timbers Plantation in the longleaf pine woods outside Tallahassee.
As the first birds approach the tower, its steady red glow seems to draw them in. Disoriented, they circle the structure like June bugs around a porch light. They can't break away. As more migrants join the milling flock, birds begin to smack into the tower itself, the guy wires that support it, and each other. Exhaustion overtakes them and the collisions increase. An opportunistic screech owl, lured by the migrant's distress calls, snatches some of the casualties before they hit the ground.
At dawn, the grass beneath the tower is littered with the small corpses of the southbound travelers: A pickup truck pulls up, and Herbert Stoddard begins to search the ground for whatever the predators and scavengers have left. As he will every migration season for the next 15 years, Stoddard inventories the night's carnage. After his death, others will continue the project for another 10 years. Eventually, the toll will add up to 42,000 individual birds of 189 species.
Some incidents were worse than others. On one particularly bad night early on in the study, the WCTV tower claimed 7000 birds. Large kills were associated with overcast skies, north winds, and passing cold fronts. The lunar cycle played a part, with more deaths occurring during the dark of the moon.
The Tall Timbers chronicle and physician Charles Kemper's 38-year documentation of tower kills near Eau Claire, Wisconsin have given us two of our best data sets on bird mortality at communications towers, but beyond them it's hard to quantify the losses precisely. Most of the long-term studies have been in the eastern United States; there's very little data from outside North America. "The estimate is 4 to 5 million deaths per year at the low end," US Fish and Wildlife Service biologist Al Manville says. "It could be as high as 40 to 50 million."
As new technology--cell phones, high definition television--drives a proliferation of towers, the toll, whatever it is now, is likely to rise. Scientists are still trying to pin down what causes the phenomenon, while environmentalists contend with a frustrating maze of federal regulatory agencies.
Towers are just one hazard migrant birds face on their journeys to and from their wintering grounds, and perhaps not the worst. Paul Kerlinger, author of How Birds Migrate and columnist for Birder's World, provides some staggering estimates. Collisions with windows may kill between 100 million and a billion birds each year, with electrical transmission lines accounting for another 150 million and motor vehicles 60 to 80 million. The annual loss to house cat predation may exceed 100 million.
Still, the tower kills are troubling. Most of the victims are passerines (songbirds) that migrate to the New World tropics, flying by night to reduce the risk of predation: A much-publicized mass kill of Lapland longspurs--prairie birds that winter in the Great Plains--in Kansas in 1998 appears to have been an anomaly. "It's a bizarre misrepresentation of what occurs," Kerlinger says. The longspurs perished at a 420-foot-high tower in a January blizzard. But sodium vapor lamps at a nearby natural gas pumping station may also have attracted or disoriented the birds.
Neotropical migrants as a group have experienced declines due to habitat loss and fragmentation on both breeding and wintering grounds, and there is serious concern for such species as the cerulean warbler and wood thrush. …