Acoustic beacons to prevent birds from colliding with buildings: this is how these scientists have reduced their risk of mortality

A walk through New York, Dubai, Tokyo or Shanghai is enough to prove it: we like our cities to grow up. For decades, for reasons of space and the price of land – probably also in a demonstration of power with interesting Freudian implications – we have tried to stretch the ceiling of the metropolis to the maximum. We love. To the birds, less. The glass facades of buildings, communication towers and power lines often end up becoming obstacles against which a good number of birds lose their lives. It is estimated that Only New York is charged, each year, about 200,000.

In their search for formulas capable of avoiding this devastating impact, biologist Timothy Boycott, from William & Mary College, and his team have come up with a formula that, for the time being, and at least based on the results of their preliminary tests, seems to point in the right direction: install “acoustic headlights” that take care of emitting short bursts of a special noise, recordings –detalla Science Alert– “broad spectrum, a kind of static and hissing sound”.

A good soundtrack, the best ally

In an article published in spring on the official William & Mary website, it is pointed out how the “hiss” tested at two frequencies: 4 to 6 kHz and 6 to 8 kHz. The first fork matches the hearing range of many birds; the second was chosen to stand out from the ambient noise, such as the hum of traffic or the murmur of the waves. The test was carried out in the vicinity of communications towers located on the coast of Virginia, in the USA, for six days in three-hour sessions. To reinforce the monitoring, they installed cameras that pointed to various areas. The place of the experiment was not accidental either: it coincides with the Atlantic migration route.

By analyzing the videos of the 4-6 kHz and 6-8 kHz emissions and those of the control tests, the researchers identified some patterns. Both stripes were effective, but with nuances. “We saw that during the lower frequency range, at 4-6 kHz, the birds slowed further. They stayed farther apart and angled their trajectories farther, ”says Boycott. The slower speed and the change in gear would in turn reduce the risk of collision. The images also reveal how smaller birds seem to drift faster.

How effective is the “acoustic beacon”? In an article published in April on Plos One, the researchers detail that during the experiment activity around the towers decreased between 12 and 16%. Moreover, in 145 tracked flights, which experts considered “risky”, the birds slowed and deviated their trajectories to a greater extent when they were exposed to “acoustic stimuli” deployed near the turrets.

“In general, it is clear that the acoustic signal of 4 to 6 kHz that we implement reduced the risk of collision. Therefore, the use of acoustic signals to mitigate collisions in open airspace deserves a more in-depth exploration —concludes the report published in Plos One-. We tested the acoustic beacon concept in one context: flights around tall communication towers during the autumn migration. It would be of great value extend this test to other times of the year, to other landscapes and seascapes, and other structures that present collision risks. “

Despite the good starting results, there are still challenges to face. Acoustic signals can be great allies of birds, but, Boycott explains in statements collected by Science Alert, “They could present challenges to other wildlife, mask communication signals, or increase stress.” Precisely for reduce those “negative consequences”, advocate the use of “intermittent” broadcasts and always adapted to the context.

The acoustic beacon does not have to work alone either. In his Plos One article, the researchers themselves recall that other options to protect birds have already been tested, especially with visual cues, and advocate a combination of strategies to achieve a “multimodal solution”. The objective: to alleviate, as far as possible, the bleeding of birds that every year ends up defenestrated against towers, buildings or wind energy installations, an “enemy” that also usually appears in the air currents used by birds for their migrations.

Images | anatoly_l (Flickr) Y J@M€S (Flickr)