April 27th, 2012 by James Ayre
Almost seven million birds die every year in North America by running into communication towers during migration. There are 84,000 communication towers in North America, and they can rise up to 2,000 feet.
For context, the Exxon Valdez oil spill killed 250,000 birds and the height of the Empire State building is 1,250 feet.
“This is a tragedy that does not have to be,” said lead author Travis Longcore, associate professor in the USC Spatial Sciences Institute at the USC Dornsife College of Letters, Arts and Sciences.
In a study by the University of Southern California, they found that the taller a tower is, the greater the threat is. There are only 1,000 or so towers above 900 feet, 1.6 percent of the total towers, but they account for 70 percent of the killed birds.
The birds are usually not killed by the tower itself but by the guide wires that hold the tower up. Most of the fatalities appear to occur when cloud cover takes away their view of the stars, which they partly use for navigation.
The researchers also found that towers with solid red lights rather than blinking ones resulted in far more dead birds.
“In the presence of the solid red lights, the birds are unable to get out of their spell,” Longcore said. “They circle the tower and run into the big cables holding it up.”
Longcore estimated that bird mortality could be reduced by 45 percent by changing the steady lights to blinking ones. He also recommends that businesses share towers to cut down on the total numbers.
The study focused on the tall towers that are used for TV and radio broadcast, not the shorter towers used for cell phone transmission.
Source: University of Southern California
Image Credits: Longcore et al. PLoS One; doi/10.1371/journal.pone.0034025.g006, USGS
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