Billions of birds die each year from collisions with tall glass buildings, communication towers and power lines – a staggering toll that is expected to increase as cities expand outward and upward. .
A recent study suggests that there may be a way to correct our deadly mistakes – by installing “acoustic beacons” that emit white noise in short bursts, stopping migrating birds on a collision course with towering metal structures, tall buildings and maybe even wind turbines.
Field trials testing two types of sound signals reduced bird activity around communication towers by up to 16%, and researchers believe these acoustic beacons could also reduce the risk of bird collisions with wind turbines. .
Wind turbines are built to harness the energy of the same wind currents that migrating birds roam, Explain conservation biologist Timothy Boycott of William & Mary College, who led the study.
“This is an area of high potential conflict between migratory birds and human development,” Boycott said.
And this development is only expected to increase at a staggering rate.
“We are building structures at a faster rate than at just about any time in human history,” said wildlife ecologist Jared Elmore, who was not involved in the study. , Recount Audubon.
“Glass is considered a really attractive and inexpensive building material. And it’s not good for birds.”
Environmentalists have devised all kinds of strategies to reduce the number of deaths from bird collisions, patterned glass to rope curtains and laser lights. But these strategies are not always effective, possibly because birds see the world very differently from humans.
Most birds have eyes on either side of the head, facing outward, which means birds that fly with their heads down and wings up have a gaping blind spot right in front of them. Wind turbine blades that cut a sweeping path in the air also present a different displacement risk than reflective glass buildings and steel towers.
Given all of this, Boycott and his colleagues thought the sound might be a better safety warning for birds rapidly approaching an artificial structure; an idea with which some researchers in the group first tested zebra finches in captivity.
In these latest field tests, conducted during the North American fall migration, loudspeakers emitted white noise in 30-minute bursts around two communications towers on the Delmarva Peninsula on the eastern seaboard of the United States. -United.
“This is a geographic area that sees an incredibly high abundance of birds passing by,” Boycott said. “And these birds are moving south along the Atlantic flyway, heading south to the very tip of South America in some cases.”
With the speakers installed at the base of the towers, two different types of white noise were tested for six days.
“They were both broad spectrum, kind of a static, hissing sound,” Explain Boycott, with one to match the hearing range of many birds and another, at higher frequencies, chosen to stand out from the background noise.
Using cameras to capture the flight behaviors of more than 1,500 birds passing within 100 meters (328 feet) of two communications towers allowed researchers to count potential birds rescued, rather than counting lost birds. , like other studies have done.
Boycott and his colleagues recorded the birds in flight from multiple angles, analyzed the images, and found that the two sounds tested deterred birds from flying too close to the towers. But more birds moved away from the towers earlier when the low frequency sound (4-6 kHz) was projected, compared to normal conditions.
“[Birds] stayed farther from the towers and they oriented their flight paths more away from the towers ”, Boycott Remarks, which could indicate that lower frequencies are more clearly audible to birds – although this could vary from species to species.
Small birds also moved away from communication towers faster than larger birds, but based on video footage, the study did not track individual bird species. Some species are more prone to collisions, especially migratory birds which fly in large groups at night.
“Future studies would be really important to see how these differences in flight behavior actually translate into ground mortality,” Boycott add.
Previous tests have also shown that the sound alone might not deter the birds but rather alert them to the dangers ahead, so additional visual cues may still be needed. For example, a study in Norway recently found that painting a wind turbine blade black to increase visibility could help reduce the risk of a collision.
With regard to acoustic beacons, frequencies may need to be changed for birds native to other continents as well. It would also be wise to consider the impacts of man-made noise in general, since humans encroaching on the natural world are what created this situation in the first place.
“Acoustic warning signals could also present challenges to other wildlife, masking communication signals or increasing stress,” Boycott and colleagues Remark. “To reduce the unintended negative consequences of acoustic warning signals, context-dependent intermittent use can be a convincing solution.”
However, as the first proof of concept, these audible warning signals could be a promising step in the right direction.
“It would be very useful to extend this test to other times of the year, to other landscapes and seascapes and to other structures with risk of collision,” the team writes.
The study was published in PLOS A.