Birds may have inspired humans to conquer the air, but now that we share the skies each year hundreds of birds and aircraft collide, causing billions of pounds of damage and a number of fatalities. Between 1985 and 2013, these collisions were responsible for 255 deaths. This problem is the worst in airports, with the majority of strikes occurring during take-off. Not only do collisions pose a threat to humans, but migratory and resident birds are at risk because they find the habitat around airports – such as wetlands and open fields – appealing. With birds becoming ever more used to sharing our urban spaces, and air travel becoming more regular, this is an issue that needs to be solved quickly.
Many measures are used around the world in an attempt to reduce bird strikes, yet these often prove ineffective or unethical. Techniques include shooting, poisoning, live capture and relocation. Chinese airports have recently come under-fire after setting kilometres of mist nets along the runways. These capture millions of birds a year, and when the birds are left in the net they die from starvation, stress and exposure.
New research has shown that playing controlled sound may reduce the number of collisions. Acoustic communication plays a vital role in a birds’ day-to-day life. Foraging, territorially, social structure and mating often rely on a bird’s ability to sing and call to each other uninterrupted.
Previous acoustic techniques have proven ineffective in the past; loud bangs and the playback of predator vocalisations or distress calls often don’t work because the birds become used to the noises, knowing not to associate them with danger and subsequently ignoring them. However, Professor John Swaddle, visiting Research Associate at the University of Exeter, set out to interrupt the birds’ acoustic environment in a way that they wouldn’t be able to get used to.
Swaddle and his team set up speakers and amplifiers on an airfield, playing an uninterrupted, high amplitude noise, 24 hours a day for 4 weeks. This ‘sonic net’, equivalent in volume to the conversation in a busy restaurant, was designed to interfere with the bird’s ability to detect predators or alarm calls – rather than faking them as previous studies had done.
“By playing a noise at the same pitch [as predator or alarm calls], we mask those sounds, making the area much riskier for the birds to occupy,” says Swaddle. “The birds don’t like it and leave the area around the airfields, where there is potential for tremendous damage and loss of life.”
The results, published in Ecology Applications, prove promising. During the 4 weeks when the sounds were deployed there was an 82.3% reduction in bird abundance, compared to when no sounds were played. Furthermore, the researchers suggest that sonic nets could reduce the economic costs of bird strikes by 95% or more! These findings are incredibly encouraging. With further refinements sonic nets could have invaluable positive implications for airport safety and make other, less sustainable techniques, redundant.
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