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Many forces claim songbirds | Tall towers send false signals
Thousands of colorful songbirds create magic in the air as they wing their way back and forth each spring and autumn on their annual migration. That such tiny fluffs of feathers can traverse such great distances against many odds is among the reasons humans are so entranced by wild birds.
But there's another kind of airborne magic – the invisible kind thousands of broadcast and telecommunications towers send and receive – that is competing with birds for airspace. It's not the signals, but the towers themselves that have added to the growing risks migrating birds face both on their perilous seasonal journeys and in the places they live each summer and winter.
"Migratory songbirds entering the 21st century face a lot of threats," says Bill Evans, an ornithological consultant affiliated with Cornell University in New York, who also specializes in the nocturnal acoustical monitoring of migrating birds. "Collisions with telecommunication and broadcast towers are one cause of songbird death we can do something about."
Birds have died by the thousands in collisions with lighted television and radio towers around the country since the 1940s. While incidents involving massive bird kills occur infrequently, there's concern among ornithologists that bird deaths will greatly increase because of the explosive growth in the number of towers being sited in the U.S., Canada and Latin America to provide wireless services such as mobile telephones.
There's also a U.S. government mandate requiring television stations to convert to digital television by the middle of the next decade, which is already leading to the construction of more towers around the country, especially the taller ones that are thought to cause more of a collision risk for birds.
The growth in tower numbers comes when evidence shows the numbers of songbirds migrating to and from the tropics – "neotropical migrants" – have significantly declined, mostly due to habitat loss and related problems. According to the Ornithological Council, of the 124 species on the 1995 List of Migratory Nongame Birds of Management Concern in the U.S., 60 are neotropical migrants.
Unfortunately, the types of dead birds most frequently found at tower sites are neotropical species such as warblers, thrushes, vireos and flycatchers. Ironically, scientists are pretty certain about this because, armed with collector's permits, the scientists themselves and amateur bird enthusiasts have been visiting tower sites for years as favored places to gather dead birds for study purposes.
So how big an impact do towers have on bird deaths? Evans and other scientists put the estimate at a conservative two to four million songbirds a year in the eastern United States, but the overall impact of tower collisions on bird populations on a national, regional or species scale is unknown. Research projects on the subject have dwindled just when more information is needed to start forming solutions.
Despite their concern, avian researchers say tower collisions are not the major cause of songbird declines. Natural causes, such as disease or exhaustion from the rigors of migration, take a toll. Thousands of birds also can be killed in storms that occur at peak migration periods, but historically bird populations have been high enough to withstand the infrequent impact of storm deaths.
Birds also die from crashing into other manmade structures, including utility wires, buildings – especially tall, lighted buildings with reflective glass – lighthouses, fences and vehicles. Any bird observer will also note that birds opportunistically use some of these same structures as perch or nest sites.
The biggest culprits thought to be causing songbird declines are changing land uses in both North and South America that fragment the forests and grasslands various migratory species depend upon for survival. "Changing farming practices and development also contribute," says bird expert and Madison resident Sam Robbins, author of Wisconsin Birdlife.
Fragmented habitat leads to secondary causes of bird mortality that over time can make a significant dent in bird populations. For example, predators that thrive in fragmented landscapes, such as raccoons, skunks and cowbirds can cause a large increase in nest egg destruction. Predation from feral cats claims much larger numbers of songbirds – an estimated 7.8-200 million birds annually, acording to UW-Madison wildlife ecologists. Unless more information is gathered soon and appropriate actions taken, scientists believe migratory songbirds will increasingly suffer from a combination of causes driving down their abundance, including tower collisions.
"It's the cumulative sources of mortality piled one on top of another that is the cause for concern here," says Steve Ugoretz, an environmental impact project manager for the Wisconsin Department of Natural Resources who is representing the agency on a recently-formed national group analyzing the tower kill problem.
Ugoretz, Evans and others believe straightforward solutions can be found, but cooperation among broadcasters, telecommunication companies and federal and state agencies is needed.
The lights on taller towers are thought to lead to bird deaths by confusing the different cues birds use on their journeys to nesting or wintering grounds. While some birds die in tower collisions on clear nights, most bird-tower deaths occur when there is fog or low clouds. Towers featuring flashing red lights appear to confuse birds more than those with white strobe lights do.
Towers 200 feet or higher must be lit to comply with Federal Aviation Administration (FAA) regulations designed to aid safe airplane navigation. As of June 1999, more than 40,000 lighted towers and tower farms were registered in the FAA database of obstacles in the U.S. that exceed 200 feet in height.
Most species of songbirds migrate at night, flying aloft at 1,000-2,000 feet. They rely on many aids to guide them on their journey, including the sun, moon and stars, landscape features, weak magnetic fields, polarized light, barometric pressure, low-frequency sound waves, even odors.
Celestial aids and landscape features are obscured in foggy or cloudy weather. In those conditions, birds must rely on other cues to orient themselves. Lit towers disrupt these cues, just as drivers, are cautioned to avoid using their brightest headlights in fog because the light refracts off the airborne water particles, making the view of the road even worse.
Something similar may happen to birds when they fly into the lighted area surrounding a tower. Light from a tower refracts off water particles in the air. Birds use the increased visibility as their strongest visual cue for navigation. The birds keep the light at right angles to their flight to keep going in the same direction, similar to the way they would navigate in relation to natural sources of light, such as the polarized light the sun casts into the sky after sunset. The birds become reluctant to leave the lighted area.
The numbers of birds caught in such a situation can run into the hundreds and thousands during peak migration periods. As more and more confused birds funnel into the lighted area, they mill round and round uttering distress calls. Death most often occurs when the birds run into guy wires supporting the tower, hit the tower itself, or collide with other birds.
Bill Evans has witnessed songbirds flying into guy wires. He's also recorded distress calls on his acoustical monitoring equipment at towers and other sites. "Those sounds just hit you inside," he says. "They motivated me to study this more closely and try to do something about it." Evans runs a web site, www.towerkill.com, devoted to sharing information and finding solutions to the bird-tower collision problem.
According to the Ornithological Council, of the five long-term studies that have been conducted at single towers 800 feet tall or higher, annual documented mortality ranged from 375 to 3,285 bird carcasses per year (20-year average). About half the birds were found dead over many months rather than at single night catastrophes.
Kills have been observed at towers all over the eastern United States, including Florida, Tennessee, Kansas, New York, New Hampshire and West Virginia. The most well-known series of tower kill incidents – documented in a set of data Evans calls "phenomenal" – occurred right here in Wisconsin as observed by Dr. Charles Kemper, a physician and bird enthusiast who is also a past president of the Wisconsin Society for Ornithology.
From 1957-1994, Dr. Kemper regularly collected dead birds at a TV tower in Eau Claire. During that period the kill totaled 121,560 birds of 123 species. A thousand or more birds were killed at this tower on each of 24 nights since 1957. A record 30,000 birds were estimated killed on one night in the mid-1970s.
"I originally began collecting these birds because they provided a wonderful tool to help us know when each bird species migrated," he says. "The staff at the station really weren't aware of the numbers of birds killed at their tower because the staff were rarely there at dawn back then, which I learned was the best time to pick up the birds before predators got them."
Dr. Kemper noticed bird deaths dramatically rose after the station put up a taller tower in 1956. The new one was about 1,000 feet high, twice the height of the previous tower. "One day the county public health department called because all these dead birds were being found near the tower site; they thought the birds might have been dying from a type of disease."
Dr. Kemper said he didn't inform Eau Claire TV staff of what he found over the years because he wasn't sure how important it was for them to know and he didn't want to embarrass them by telling them. Today, WEAU has two towers – the old, 960-foot one within the city and the station's main, 2,000-foot tower located 30 miles away in rural Fairchild.
Cheri Weinke, manager of WEAU-TV for 19 years, says to her knowledge very few tower-bird kill incidents have occurred at her station in recent years, an observation shared by Dr. Kemper, who says bird deaths at the Eau Claire tower dropped after the 1960s for unknown reasons. According to some ornithologists, the drop could be due in part to the overall decline in migrating songbird numbers monitored since then. Dr. Kemper says another factor could be the growth in the number of towers that has occurred since the 1960s, which could be dispersing bird deaths at towers over a wider area.
"Predators are very efficient at picking up these bird carcasses, so it's possible bird deaths may not even be noticed by TV station employees much of the time," he says. Kemper suggests predation could be another reason why few birds are being found at the Eau Claire tower. "A colony of gulls established itself near that tower in recent decades, and they may be scavenging the bird carcasses before anyone else sees them," he says.
The number of bird deaths could go up around Wisconsin and the U.S. because more towers, including taller, lighted ones, are being constructed or retrofitted to serve the broadcast and telecommunications industries. At the current rate of construction, the Ornithological Council says the number of towers in the U.S. will likely double to 80,000 by 2010. A similar expansion is underway in Canada and Latin America.
The Telecommunications Act of 1996 is partly responsible for the U.S. tower explosion by accelerating construction of a massive telecommunications infrastructure. According to industry information in a Federal Communications Commission (FCC) news release, numbers of customers using mobile phone services, which rely on "personal communication system" (PCS) towers, already has rapidly increased from 24 million subscribers at the end of 1994 to over 78 million in 1999.
The wireless gold rush is well underway in Wisconsin, says John Pohlman, an environmental reviewer with the DNR's Bureau of Endangered Resources. Company representatives who have contacted him talk about trying to locate a PCS tower every five miles to improve transmission to customers.
Pohlman uses information in the DNR's Natural Heritage Inventory (NHI) to evaluate the impact of proposed projects around the state, such as tower sitings, and to protect rare resources. The inventory maintains data on the locations and status of rare species, natural communities, and natural features in Wisconsin.
"Requests for checks of our Natural Heritage Inventory from the telecommunications industry have been almost out of control, especially over the last year," he says. "They're the number one request we get by far. Volume is so high we've trained some of the industry consultants to handle initial NHI screenings themselves, so that the DNR examines only those that require more analysis."
Pohlman says PCS towers pose little threat to rare plants or animals as a consequence of disturbing the soil. "A lot of these towers are located in previously disturbed areas, with most located along major roads," he said. As might be expected, volume is highest in southeastern Wisconsin where the state's population is highest. He has found that the height of some proposed towers is increasing, but the number of towers going up is being minimized somewhat because telecommunications equipment is being sited on existing structures about half the time.
"The main environmental problem we are watching out for with telecommunications towers are the deaths of birds and bats," he says.
Digital TV will add even more towers to the landscape, including taller ones. Digital TV (DTV) is a new broadcast technology that will transform TV, allowing broadcasters to offer free TV with movie-quality picture and CD-quality sound. Digital technology will also enable the rapid delivery of a large amount of informational services over TV sets and free up valuable broadcast spectrum for use by other information and communication services.
According to the FCC, which regulates interstate and international communications by radio, television, wire, satellite and cable, all TV stations will need new transmitter, antenna and production facilities. Some TV stations will have to modify their towers or build new ones for their DTV antennas. Broadcasters may need to get local or state government approvals regarding zoning, structural engineering, construction safety and other issues.
DTV towers are already poking into the sky around the U.S. because of aggressive federal deadlines driving the digital conversion. Stations making up the top 10 television markets – reaching 30 percent of U.S. households – were given until May, 1999 to go digital; stations in the next 11 to 30 markets, which reach another 53 percent of U.S. households, were given until November, 1999.
Wisconsin TV stations occupy smaller markets and have more time to comply with federal deadlines. John Laabs, director of the Wisconsin Broadcasters Association, says Wisconsin has 40 commercial and noncommercial television stations that must adopt digital transmission by May, 2002 for commercial stations and a year later for non-commercial stations.
"Each station will have to decide for itself whether it needs to build a new tower, use its existing one or team up with other stations that also need digital antennas," he says. "Those decisions will be based mostly on competitive factors and cost."
Laabs says not all stations broadcasting in Wisconsin will need to build a new tower. Some stations, such as several in Madison, will use a "candelabra," which consists of one tower carrying multiple antennas for multiple stations. Some new towers could be taller if a station decides to be more competitive by broadcasting its signal a longer distance. He predicts the total number of TV transmission towers in the state following the digital conversion will approach 50 to 60 from the current 40.
The digital shift does not come cheap. Smaller stations will need to invest $3 million to $6 million, Laabs estimated, while the price tag at Milwaukee stations will total around $6 million to $12 million.
A similar digital transition for radio is less clear, except that it won't be as costly, Laabs said. The FCC has not okayed a single standard for transmitting radio digitally, so stations may decide to do it on their own for competitive reasons or wait for an FCC mandate.
Despite all the information available about bird deaths caused by towers, the problem was little recognized outside ornithological circles. In 12 years as head of the Wisconsin Broadcasters Association, John Laabs said he never knew the problem existed until he got a call in 1999 from the DNR's Steve Ugoretz inquiring about the issue.
Bird expert Sam Robbins says television stations didn't want people to know that TV towers killed birds. "People who man towers kept quiet about these bird deaths. They didn't want to alarm the public on the extent of this problem," he said.
Bill Evans has a different take. "I blame the ornithologists – they've known for more than 50 years that TV towers kill birds, but they sure didn't make the broadcast and telecommunications industries aware of the problem until recently," he says. Even his web site says the situation "has blind-sided everyone – conservationists, industry and federal agencies alike."
The problem finally came to the attention of federal agencies in the late 1990s, even though new broadcast and telecommunications towers had already begun sprouting up all over the country. A 1998 issue of Bird Calls, the newsletter of the American Bird Conservancy's Policy Council, notes that addressing the tower kill issue has been complicated by a separation of authority within the FCC, where wireless communications fall under one bureau, and radio and TV in another. The agency is required to pay close attention to National Environmental Policy Act regulations covering such environmental risks as floodplains or historic sites, but bird-tower deaths have entered into few if any FCC licensing decisions, the council claims.
In 1998, the American Ornithologists' Union, the Association of Field Ornithologists, and the Cooper and Wilson ornithological societies approved a joint resolution strongly encouraging the U.S. Fish and Wildlife Service to work with the FAA and FCC to study the magnitude of the tower kill problem and assess the need for a national environmental impact statement.
The Fish and Wildlife Service used its authority under the federal Fish and Wildlife Coordination Act to bring federal agency officials together to address the concerns. Also on the group are representatives of the broadcast and telecommunication industries, bird organizations, universities and state government agencies. The DNR's Ugoretz is a member of this group, which met for the first time last summer.
"Right now, Wisconsin has an excellent chance of getting a leg up on this issue to help contribute to a national consensus on solutions," Ugoretz says. John Laabs says he'd be willing to discuss migratory birds and tower collisions further with his organization's board and with the DNR. "If it really is an issue, then there ought to be a concern," he says. "My industry needs more information about this issue."
Though the issue finally gained momentum late in the digital TV and telecommunications rush, solutions may not be far off, and some actions, such as co-location of towers, are already being taken. In general, solutions lie in making towers more "bird-friendly" by siting towers carefully, adjusting tower design where possible to eliminate the need for guy wires and adjusting tower lighting to make it less attractive to birds.
Tower lighting – When fog or clouds dissipate around towers known to kill birds, observers have noted that the birds previously flying confusedly around the lit towers soon reorient themselves and fly off. That silver lining makes researchers believe that changes in tower lighting might spare birds even as more towers go up. Certain colors of lights or changes in flashing intervals may confuse birds less.
To conduct such research, the FAA could give tower owners permission to change lighting systems so researchers can compare effects of different types of lights and illumination intervals.
"We'd certainly change our tower lighting if the FAA and FCC allow us to make changes, but the lighting is there to protect people in airplanes, so we wouldn't do anything to adjust lighting without federal approval," WEAU-TV station manager Weinke says. Local residents must be factored into any lighting plan for towers located in or near residential areas, she notes, as certain types of outdoor lighting can be annoying to people.
Because stations already facing the high costs of converting to DTV may be reluctant to change lighting even with federal agency approval, John Laabs suggests regulators could perhaps give stations more time to change lighting rather than make any mandate immediate. "More time to comply would minimize the already high costs stations expect to experience in their digital conversion," he says.
Another possible solution the aviation and communications industries could explore, Dr. Kemper suggests, is the use of satellites to map tower positions and heights, possibly reducing the need for tower lights while still ensuring aviation safety.
Tower height and design – Guy wires are the main cause of bird death at tower sites, so reliance on self-supporting or other tower designs may offer solutions. Lower tower heights remain a possible option as well. Dr. Kemper believes the FAA should consider towers less than 500 feet tall, which may spare many birds, though little formal research has been conducted on the impact of shorter towers on bird deaths.
"The federal government already has a policy against tall towers," he says. Although there is no absolute height limit for antenna towers, both the FCC and FAA frown upon structures over 2,000 feet above ground as being "inconsistent with the public interest" and a hazard to air navigation. Local opposition already has arisen in some states where very tall TV towers are being proposed. The burden is on applicants to overcome the federal agencies' position. DTV stations do not always require very tall towers, the FCC says – the height requirement is no different than for analog TV (the kind currently being broadcast).
Tower sighting – Tower owners could co-locate their equipment where possible. Federal regulation does not mandate the co-location of communication antennas nor does it require that communication companies show that no other existing structures suitable for antenna siting are available. Since broadcast towers are very expensive to build, stations already try to consolidate towers at existing sites, Weinke said. WEAU won't be building a new tower, she says; the station plans to retrofit one of its existing towers to provide digital television.
Tower sitings in sensitive areas also could be limited. While the Department of Natural Resources in Wisconsin has little or no regulatory authority over tower siting, the agency has encouraged telecommunication representatives to consider alternatives if a tower siting proposal may affect natural resources. "One firm wanted to locate a new telecommunications tower near the southern unit of the Kettle Moraine State Forest, but we said we really preferred that they do something else," Pohlman says. With a few phone calls, he found a nearby existing tower. After a few months and an ownership change, a deal was worked out and the original firm ended up co-locating its equipment on the existing tower.
The federal Telecommunications Act of 1996 forbids towns from barring towers completely and denying access. But the law does allow local governments great leeway in restricting the height, appearance and location of towers. A Portage County ordinance that went into effect last year to protect birds and other natural resources prohibits telecommunications facilities from being sited in floodplains, wetlands, shorelands and conservancy-zoned districts.
Bird-tower research – Standardized surveys coordinated across many towers in a flyway or multistate geographic region could help researchers determine the magnitude of the tower kill problem and discover which types of towers and lighting systems are the least harmful. Tower owners also could give scientists permission to study bird mortality at their towers, and the FCC could require owners to allow tower research to generate enough national data to evaluate the effectiveness of various prevention methods.
"A couple years of research could yield fairly simple solutions that could spare the unnecessary death of lots of birds," says Bill Evans. He hopes industry could help pay for some of the research.
Steve Ugoretz says nonprofit birding and conservation organizations may also wish to contribute to study efforts. conserve bird populations in North, Central and South America, and prevent more songbird species from becoming threatened or endangered.
Wisconsin – home to many distinguished bird experts and thousands of bird lovers – has a strong history of taking actions to protect wild birds and their habitats. Ugoretz believes cooperation among broadcasters, telecommunication companies, government agencies, bird experts and the public can shape an intelligent national policy soon so actions can be taken this decade.
Science writer Wendy K. Weisensel works for DNR's Bureau of Communication and Education in Madison.