A new study by the Federal Aviation Administration has identified ways to reduce bird mortality at communication towers throughout the United States without compromising airplane safety.
Previous studies concluded that large numbers of migratory birds are killed when they become attracted to the steady-burning or slowly pulsing (i.e., non-flashing) lights on communication towers that alert pilots to the tower’s presence.
“Past research has comprehensively documented the phenomenon of migrating birds confusing certain nighttime tower lighting with stars. The birds become trapped in a corridor or cone of light and either collide with the structure or circle repeatedly until they drop exhausted to the ground, where they then become easy targets for predators. This new FAA study offers a solution to reduce that mortality, and as such, provides a major step forward for the conservation of our declining songbirds,” said Darin Schroeder, Vice President for Conservation Advocacy for American Bird Conservancy.
American Bird Conservancy led a coalition of other environmental organizations (including Defenders of Wildlife and National Audubon Society) working for over ten years with communication industry groups (including CTIA – The Wireless Association, National Association of Broadcasters, National Association of Tower Erectors, and PCIA – The Wireless Infrastructure Association) and the Federal Communications Commission (FCC – the government agency that licenses towers) to reduce bird mortality at communication towers.
In 2007, those groups jointly requested that the Federal Aviation Administration (FAA – the agency that requires towers over 199 ft. tall to be lighted according to certain approved configurations) conduct a study to assess the relative visibility of different lighting schemes to pilots. The groups hoped that the FAA would then be able to recommend certain configurations that were highly visible to pilots yet safer for birds.
The FAA began the study in 2009 and looked at several key issues, including: the effects of flashing the normally steady-burning red “obstruction” lights that go up the side of the tower simultaneously with the flashing lights on top of the tower; the effects of omitting the red side-marker lights altogether; and whether new lighting technologies, such as LED, offer any benefit over conventional, incandescent lights. The FAA Airport Technology Research and Development Team conducted a series of flight evaluations to compare the lighting schemes on several communication towers in the northern Michigan area.
The results showed that flashing the side-marker lights was acceptable for small towers (151 to 350 feet in height) and that they could be omitted altogether on taller towers (over 351 feet) so long as the additional bright flashing lights were operational. The optimal flash rate for the lights to flash was determined to be between 27 and 33 flashes per minute. Flashing at slower speeds did not provide the necessary visibility for pilots at night without the additional steady-burning side-marker lights. Flashing at faster speeds meant that the lights were not off long enough to be less of a hazard to migratory birds.
The study also found that LED and other types of “rapid discharge” lights provide a more attention-getting signal for illuminating obstructions compared to incandescent light fixtures. The near-instant on and off characteristics of LEDs (as opposed to the relatively slow-fading, slow-brightening glow of an incandescent bulb) make them easier to locate from greater distances, and allow the precise control of the flash rate and synchronous operation with other fixtures. The pronounced off cycle of LED fixtures would also make them less attractive to birds. LED lights also use less electricity, providing a long-term benefit to tower owners and operators.
Based on the results of this research, the FAA proposes to make specific changes to the obstruction lighting standards, including a proposal to omit or flash steady-burning red lights from several obstruction lighting configurations.
There are more than 100,000 towers that are lighted in the U.S. Some of these towers can reach 1,700 ft. or more in height. A recent study estimated that seven million birds are killed each year in tower collisions, the majority night-migrating songbirds.
Logo courtesy of the American Bird Conservancy, image courtesy of Mike Parr