PLoS ONE. The 84,000 towers provide TV and radio frequencies and can be as high as 2,000 feet. As Science Daily notes, 250,000 birds were killed in the Exxon Valdez oil spill and the Empire State Building is 1,250 feet high.
The study, entitled “An Estimate of Avian Mortality at Communication Towers in the United States and Canada,” found that taller towers posed the greatest threats to migrating birds. Only 1.6 of the towers — about 1,000 — are taller than 900 feet but they killed 70 percent of the birds, some 4.5 million a year.
Among the birds who are killed are the Common Yellowthroat and the Tennessee Warbler, insect eaters who help to keep forests healthy.
It is not the freestanding towers that are actually the cause of death for millions of birds but the guy wires, the dozens of cables that keep the structures standing. In bad weather, birds fly lower under the cloud cover, which also blocks out navigation cues like stars so that only the blinking or static red lights of the towers are visible. The steady red lights result in more dead birds, says the study’s lead author Travis Longcore, associate professor in the USC Spatial Sciences Institute at the USC Dornsife College of Letters, Arts and Sciences:
“In the presence of the solid red lights, the birds are unable to get out of their spell. They circle the tower and run into the big cables holding it up.”
The researchers started collecting and analyzing data from field studies starting in 2005. They calculated average bird mortality by looking at the height of towers, the guy wires and the types of lights.
According to Longcore, just changing the continuously burning lights on the 4,500 towers greater than 490 feet tall (about 6 percent of the towers) could reduce mortality by some 45 percent, for some 2.5 million birds.
In addition, the study called on businesses to share towers to lower their number and also to build more freestanding towers, so the need for guy wires is lessened. Consumers also need to realize that our seemingly insatiable demand for strong and clear TV and radio frequencies is contributing to the deaths of millions of birds. Said Longcore,
“This is a tragedy that does not have to be …One of the things this country has been great about is saying we care about not losing species on our watch. With these towers, we are killing birds in an unnatural way. This is senseless.”