Billions of birds die each year from being hit by tall glass buildings, communication towers and power lines as cities grow.
A recent study suggests that there could be a way to fix our mistakes by installing acoustic lighthouses that blast white noise in short bursts and stop birds from colliding with tall buildings.
Field trials testing two types of sound signals reduced bird activity around communication towers by up to 16 percent, and researchers think these acoustic lighthouses could reduce the risk of birds colliding with wind turbine, too.
The study was led by Timothy Boycott of William & Mary College.
Boycott says that it's an area of high potential conflict between birds and humans.
The development is set to increase at a staggering rate.
"We're building structures at a faster rate than we've ever done before," said wildlife ecologist Jared Elmore, who was not involved in the study.
Glass is seen as cheap and attractive. That's not good for the birds.
The death toll of birds has been reduced by the use of patterned glass, rope curtains, and laser lights. Birds view the world differently than humans.
Birds have eyes on either side of their heads, which means they have a blind spot right in front of them.
The idea of sound being a better safety warning for birds was first tested with captive zebra finches.
In these latest field trials, conducted during the fall migration of North America, speakers pumped out white noise in 30-minute bursts around two communication towers on the Delmarva Peninsula.
Boycott says that the area sees an incredibly high amount of birds moving through. The birds are moving southward along the Atlantic migratory flyway, headed as far south as the tip of South America in some cases.
Two different types of white noise were tested over the course of six days.
"They were both broad-spectrum, a kind of staticky, hissy type sound, and they were chosen to stand out against the background noise," says Boycott.
Using cameras to capture flight behaviors of more than 1,500 birds passing within 100 meters of two communications towers allowed the researchers to tally potential birds saved, as opposed to counting birds lost, as other studies have done.
When the lower frequencies were projected, more birds steered clear of the towers.
" Birds stayed farther away from the towers and they adjusted their flight trajectory away from the towers more," Boycott said.
The study did not track individual species of birds because it relied on video footage. Birds that fly in large groups at night are more prone to collide.
Future studies would be important to see how the differences in flight behavior translate to mortality on the ground.
Sound alone might not divert birds but rather alert them to dangers ahead, so additional visual cues may still be needed. A study in Norway found that painting a wind turbine blade black could help reduce collision risk.
Native birds on other continents may need to be adjusted for acoustic lighthouse frequencies. Humans encroaching on the natural world is what created this predicament, so it would be wise to consider the impacts of artificial noise in general.
Boycott and colleagues note that acoustic warning signals could present challenges to other wildlife, masking of communication signals or increasing stress.
The audible warning signals could be a promising step in the right direction.
Extending the test to other times of the year would be a great benefit.
The study was published in a journal.
