Nearly 7 million birds are killed annually while migrating from Canada and the United States to Central and South America due to run-ins with communications towers, according to a research article published late last month in the journal PLoS ONE.
Television and radio towers, particularly the guywires used to hold up the structures and non-blinking red lights used to warn off aircraft, are the chief culprits, says Travis Longcore, lead author and associate professor in the USC Spatial Sciences Institute at the USC Dornsife College of Letters, Arts and Sciences.
Broadcast towers in particular are the most responsible for bird deaths because of their extraordinary height when compared to other communications towers.
“The risk of these towers to the birds goes up with their height. So the taller the tower, the greater the probability it gets up to the elevation, the altitude, where the birds are migrating,” says Longcore. TV and radio towers account for 4.5 million annual avian deaths, 70 percent of the total, he says.
The article, “An Estimate of Avian Mortality at Communication Towers in the United States and Canada,” is based on the findings of hundreds of other researchers who have collected and counted bird carcasses under communications towers beginning with initial work in 1949. The study brings together the longer term records at individual towers and ends up with 38 towers, used to create a relationship between tower height and the number of birds killed each year.
Most avian tower-related deaths result from birds flying around the towers after they’ve been attracted to and mesmerized by the non-blinding, red lights.
“In the presence of those solid lights birds are unable to get out of their spell, as it were. They circle the tower and they run into these big cables that are being used to hold the tower up,” says Longcore.
The more effective way to reduce bird deaths would be to change the light scheme used on towers, says Longcore. If the tallest 6 percent of towers were to convert from solid to flashing lights, avian mortality resulting from towers would plummet by 45 percent, a mortality reduction of some 2 million to 3 million birds, he says.
Other steps include sharing tower space to reduce the overall number of broadcast towers erected and building more freestanding broadcast towers, says Longcore.
“If you can design towers that are self-supporting without guywires you should dramatically reduce mortality at those towers,” he says.
Note: A video interview with Travis Longcore about the findings is available on the USC website.