Communications Towers and Migratory Birds

The population levels of many of North America’s migratory birds have declined dramatically throughout the latter half of the 20^th century, causing grave concern among land managers and biologists. These declines are thought to be due mainly to human-induced factors, such as habitat destruction, habitat fragmentation, pesticide use, and shooting. While some of these factors, such as pesticide use and uncontrolled shooting have decreased in the past few decades, other negative factors have been on the rise. The explosive growth of the communications tower industry, as well as unabated habitat loss due to development, are likely two of the more recent causes for the continuation in the decline of many migratory birds.

The Service is becoming increasingly concerned about the effect of communications towers on migratory birds, particularly guyed towers and towers over 200 feet tall. All native migratory birds (e.g., waterfowl, shorebirds, birds of prey, song birds, etc.) are afforded protection under the Migratory Bird Treaty Act (40 Stat. 755; 16 U.S.C. 703-712). Communication towers and antennas may pose a hazard to migratory birds in flight and may pose a threat to nesting birds attracted to the site, depending on tower and site characteristics. Tower characteristics, such as height, physical design (e.g., guyed, self supporting lattice, or monopole), lighting, and site location are factors in the equation concerning tower-induced bird mortality. Towers exceeding 200 feet in height and particularly towers that are supported by guy wires are expected to have a greater impact on migratory birds than shorter, free-standing towers and co-located towers.

Research and monitoring efforts have indicated that communication towers may be taking a devastating toll on our continent’s migratory birds. It is estimated that millions of birds are killed by communications towers in the United States each year (The Ornithological Council, 1988). There have been documented occurrences of hundreds or thousands of birds colliding with towers in single events during peak migration periods (Norman, 1987; Roberts and Tamborski, 1993; Anonymous, 1998). The most devastating bird-tower collisions usually have occurred at night during conditions of low visibility, though large numbers of birds have also collided with towers at night during clear weather and during the day under foggy conditions. There are also documented occurrences of birds congregating around towers with aviation warning lights while migrating at night during inclement weather. During these events, birds apparently have become disoriented by the tower lights and have repeatedly circled the towers until they collided with guy wires, each other, or the ground, or died from sheer exhaustion. Due to the growth of the cellular phone and Personal Communication Service (PCS) industry, it is now estimated that new tower construction (over 200 feet) has accelerated to over 5,000 per year, so it is likely that bird mortality due to collisions with towers will only increase in the foreseeable future.

A Communications Towers Working Group composed of government agencies, industry, academic researchers, and non-governmental organizations has been formed to develop a research protocol to study the problem of bird-tower strikes and to determine how to best construct and operate towers to minimize bird strikes. Until the research studies are completed, the Service recommends voluntary tower siting guidelines to be used to reduce the impact of communications towers on migratory birds protected under the Migratory Bird Treaty Act and the Endangered Species Act. In order to obtain information on the usefulness of these guidelines in preventing bird strikes, and to identify any recurring problems with their implementation which may necessitate modifications, the Service requests to be advised of: 1) the final location and specifications of proposed towers, 2) which of the measures recommended for the protection of migratory birds would be implemented, and 3) if any of the recommended measures can not be implemented, why they were not feasible.

Information on tower kills, including mechanisms, studies, literature, bibliographies, legislation, links, and summaries by state, is provided on the following website: http://www.towerkill.com. A good discussion on the effects of lighted structures and migrating birds can be found in the 1996 publication by the World Wildlife Fund and the Fatal Light Awareness Program, Collision Course: the hazard of lighted structures and windows to migrating birds. Other useful information, including a bibliography on bird kills at towers and other man-made structures, can be found here: http://migratorybirds.fws.gov/issues/towers/towers.htm.

Measures Recommended for the Protection of Migratory Birds

We strongly recommend that sites selected for communications towers and other projects not impact wetlands and riparian areas, and be located as far as practical from these areas. Wetlands and riparian areas are high priority fish and wildlife habitat, serving as important sources of food, cover, and shelter for numerous species of resident and migratory wildlife. Waterfowl and other migratory birds use wetlands and riparian corridors as stopover, feeding, and nesting areas. Migratory birds tend to concentrate in or near wetlands and riparian areas and use these areas as migratory flyways or corridors, which could potentially exacerbate the documented problem of birds being killed by flying into and striking the communications towers. If unavoidable wetland impacts would occur after every effort has been made to avoid such impacts, the appropriate U.S. Army Corps of Engineers office should be contacted to determine if a permit is necessary prior to commencement of construction activities.

The Service strongly recommends that communications tower companies co-locate new communications devices on existing towers or other existing structures whenever possible to limit the amount of airspace and landscape impacted by communications towers. Secondarily, we recommend that self-supported towers (e.g. lattice) or monopole towers be used instead of guyed towers, as guyed towers have been shown to be more detrimental to birds. The narrow diameter guy wires are apparently difficult for migrating birds to see both night and day, and guyed towers impact a much greater volume of airspace than non-guyed towers. We understand that the use of non-guyed towers instead of guyed towers may cause an increase in the materials and labor costs associated with new tower construction in some instances. However, it is a violation of the Migratory Bird Treaty Act to kill or attempt to kill non-game migratory birds at any time. Therefore, it would be in the best interest of the communications tower industry to do all it can to reduce bird-tower strikes before the problem becomes severe enough to result in management action or legislation. By developing a more environmentally-sensitive set of tower construction guidelines, individual tower companies could potentially realize a financially-rewarding Public Relations benefit as well.

We also recommend that new towers should be limited to 199 feet tall or less whenever feasible, as increased tower height is known to be related to bird mortality. The FAA also requires aviation warning lighting for towers 200-feet tall and taller, and these lights have been reported to confuse and attract birds migrating in inclement weather conditions, which can compound bird mortality problems.

Additionally, we suggest that all proposed communications projects be located in previously cleared areas, urban or suburban developed areas, road or utility right-of-way, fallow fields or pastures, landscaped areas, or essentially any area that has already been disturbed and would require little or no clearing of native vegetation. Locating communications projects in these previously disturbed or developed areas should not only save money, but may help to expedite the review process for potential impacts on federally listed species because many of the threatened or endangered flora and fauna are associated with relatively undisturbed areas or sites where remnant pockets of native vegetation and/or wetlands are present. Therefore, projects located outside of, or far from, these areas are significantly easier to determine if endangered species or their habitat could be potentially impacted by proposed development activities.

We encourage the communications tower industry and environmental consulting agencies to collaborate with the scientific community to find solutions to the problem of bird-tower strikes. These collaborations may take the form of open communication, sharing of information on tower designs and bird strikes, access to towers to conduct bird casualty surveys and to test methods to reduce bird strikes, and voluntary funding of meaningful research.

References

Anonymous, 1998 (29 January). Bad weather causes Syracuse bird kill: as many as 10,000 Lapland Longspurs apparently crashed into radio towers in fog. Wichita (Kansas) Eagle. http://newslibrary.infi.net/wichita/.

Norman, J. L. 1987. Synopsis of birds killed at the Coweta, Oklahoma, TV Tower, 1974 – 1984. Bull. Oklahoma Ornithological Soc. 20: 17 - 22.

Ornithological Council, The. 1988. Communication towers and avian mortality. http://nmnh.si.edu/BIRDNET/NOAC98Res.html#radio.

Roberts, R. E., and C. V. Tamborski. 1993. Blackpoll warbler mortality during fall migration at a tower in southeastern Florida. Florida Field Nat. 21: 118 – 120.