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Features

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

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. The American Bird Conservancy reports that 52 of the 230 North American species documented as tower casualties are on either the Partners in Flight Watch List or the US Fish and Wildlife Service’s (FWS) Nongame Birds of Management Concern List. One declining species, the Tennessee warbler, is the third most common tower victim, after the ovenbird and the red-eyed vireo. (Although the Conservancy’s report mentions the endangered red-cockaded woodpecker, the two deaths cited do not constitute a major mortality factor for this non-migratory bird).

We’ve known for years that birds are drawn to lighted structures. “Folk who were in grief came to my wife like birds to a lighthouse,” says Dr. Watson in Conan Doyle’s The Man with the Twisted Lip. Mass deaths were recorded at electric light towers in Illinois as far back as 1886; the first fatalities at a communications tower took place at Baltimore in 1948. But scientists are only beginning to figure out why illuminated communications towers are so dangerous.

Avian physiologist Robert Beason at the University of Louisiana at Monroe has speculated that what attracts birds to lights is a hard-wired escape response, a tendency to fly toward the brightest part of the night sky. “Flying towards the moon would simply get the bird above any fog or low-lying clouds and out of any potential problems,” Beason explained at a Cornell workshop in 1999.

Seeing red
The color of the light and its duration (steady versus flashing or strobing) seem significant. At a conference on Ecological Consequences of Artificial Night Lighting in Los Angeles last February, Clemson University ornithologist Sidney Gauthreaux described an unpublished study from the late 1980s comparing migrant behavior near a tower with white strobe lights, a tower with steady red lights, and a towerless control area. The highest count of birds was near the red-lit tower, where they showed a greater tendency to pause, hover, or circle than birds passing the tower with the white strobes. Both towers were blown down by a hurricane before the study could be repeated.

Why should red lights affect behavior more than white lights? “Birds’ magnetic compasses seem to break down in red light,” Gauthreaux told the Los Angeles conference. Bob Beason’s research points to a linkage between birds’ sense of sight and the magnetoreceptors in their brains. Other scientists had found that migratory species such as Australian silvereyes and European robins become disoriented under red light, losing their normal vectors. Where humans have three types of color-sensitive cone cells in their retinas, birds have from four to six types, including some that can sense ultraviolet light. Sensitivity is greatest to long wavelengths in the red portion of the spectrum. Beason’s work with bobolinks indicates the ophthalmic nerve carries magnetic navigational information from the eye to the brain. So it seems reasonable that red light could drown out the birds’ magnetic sense, although the precise mechanism is still unclear. Under cloudy skies, without astronomical cues to rely on, a faulty compass could have fatal consequences.

Al Manville thinks the flash duration may also be critical in pulling birds to a lighted tower. Preliminary studies suggest that the longer the pause between blinks or flashes, the less the light attracts birds.

How many agencies does it take to change a light bulb?
If the lights are in fact the problem, you would think it would be easy enough to address. But this is where things become complicated, and regulatory agencies with different constituencies and missions come into conflict.

The Fish and Wildlife Service is legally mandated by the Migratory Bird Treaty Act of 1918 to protect migratory birds, although it has never sought prosecution of a communications company under the Act. But it’s the Federal Aviation Administration (FAA), responsible for air traffic safety, that prescribes how towers are lit, and the Federal Communications Commission (FCC) that decides on their siting. The FAA requires warning lights on all towers taller than 199 feet (the European standard is about 350 feet). As of 2000, the FCC had over 46,000 such structures in its database. The proliferation of cell phones and the Telecommunications Act of 1996, which requires that all television stations transmit digital signals by 2003, have triggered what Manville describes as “exponential growth” in new towers, many taller than 1,000 feet.

The FCC, with no in-house expertise, has historically relied on the communications industry to conduct environmental assessments for proposed towers: “a classic case of the regulated community regulating itself,” says John Talberth of the Forest Conservation Council. (Earlier this year FCC announced plans to hire a “cultural resources specialist” who will monitor industry compliance with environmental laws.) Environmentalists’ attempts to influence the process have been rebuffed. Last January the agency denied petitions by Talberth’s group and Friends of the Earth objecting to applications for 29 towers, holding that the two organizations lacked standing to intervene. The two groups filed new challenges to three tower applications the following month, the new wording emphasizing their members’ personal stake in the outcome.

But another approach to the tower issue shows promise. Following the 1999 Cornell workshop, a Communications Tower Working Group was formed with Manville as chair, Beason in charge of research, and Gauthreaux, Kerlinger, and other scientists participating. It’s an alphabet soup of over 50 federal and state agencies, nongovernmental organizations, and industry groups. In addition to F&WS, FAA, and FCC, the Department of Defense, the Environmental Protection Agency, and the Federal Highway Administration are involved.

Environmentalists are represented by the American Bird Conservancy, National Audubon Society, and Defenders of Wildlife.

One early product of the Working Group was a set of voluntary FWS guidelines for tower structure and siting. These include using white (preferably) or red strobe lights, keeping towers below the 200-foot height at which lighting is mandatory, avoiding the use of guy wires, clustering new towers within existing “antenna farms”, and locating them away from significant bird habitat and migration corridors.

Manville says some companies have been very cooperative; American Tower, for instance, consults FWS before deciding on sites. “Others are still in denial,” he adds. And some federal agencies are taking stronger steps: In three national forests in Arizona, cell phone companies are being required to monitor bird mortality at the towers they build, at their own expense.

Funding for basic research has been hard to come by. One promising industry source dried up when Cingular took over Southwestern Bell. But Manville says the National Fish and Wildlife Foundation has committed up to $75,000 in matching funds for two studies. One would assess the effects of lighting at a tower in Binghamton, New York. Researchers are trying to negotiate FAA clearance to turn off the tower’s lights in inclement weather, when no aircraft should be in the vicinity. Another proposed study would use Global Information System technology to determine where migrant birds rest and forage during the day. There’s talk of restarting Herbert Stoddard’s work at Tall Timbers, where a new tower is under construction.

“I’m hoping the industry will step forward,” says Manville, mentioning interest from the Electric Power Research Institute in underwriting research. He says Congress may also appropriate funds for the US Geological Survey’s Biological Research Division, the research arm of the Department of the Interior, targeting tower kill studies.

“We’re at a crux,” Manville sums up. “We’ve got some positive things happening [… but] there are well over 120,000 towers out there, and we don’t really know what these towers are doing to birds. We need to get a good handle on what’s going on so we can effectively deal with it.” Even if communications towers are not the greatest single threat to birds, they’re a hazard we should be able to do something about. With groups like the Fatal Light Awareness Program drawing attention to the problem and further research in the works, the night skies may become safer for the Western Hemisphere’s migrants.

Joe Eaton is a Berkeley-based nature writer.

Take Action: Urge the FCC to adopt stricter measures to protect migratory birds from tower kill. FCC, 445 12th Street, SW, Washington, DC 20554; or email the FCC’s commissioners: Chairman Michael K. Powell: mpowell@fcc.gov; Commissioner Kathleen Q. Abernathy; kabernat@fcc.gov; Commissioner Michael J. Copps: mcopps@fcc.gov; Commissioner Kevin J. Martin: kjmweb@fcc.gov.

   

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