‘Sonic net’ could reduce bird-plane collisions

People have tried all kinds of strategies to keep birds away from airports, a major site of bird-plane collisions. But loud noises and recordings of predators or alarm calls don’t work very well because the birds ignore the fake threats after awhile.

Now scientists have come up with a promising new technique called a “sonic net”. The idea is simple: Play sound that overlaps with the frequencies that birds use to call to each other. When the birds can’t communicate, they tend to stay away — and out of the path of planes.

By some estimates, bird-plane collisions cause more than $900 million in damage in the US per year. And because their habitat options are shrinking, birds often flock to the fields and wetlands around airports.

The study authors tested the sonic net strategy at three airfield sites in eastern Virginia. For about two months, the team recorded the number and types of birds at each site four times per week. Halfway through the study, the researchers turned on a speaker at one site that played constant pink noise in the 2-10 kHz range.

At the two sites where no sound was played, the number of birds didn’t change much from the first to the second month. But at the site with noise, the number of birds dropped by 82 percent in the area close to the speaker and 65 percent in most of the remaining area. And the effect was just as strong after four weeks of sound exposure.

The birds might avoid the noise because they can’t hear alarm calls from their fellow birds or the sound of predators, the authors say. And it would be hard for the birds to adapt by changing the frequency of their calls. The next step is to see if the sonic net works over an entire airport. Roberta Kwok | 5 November 2015

Source: Swaddle, J.P. et al. 2015. A sonic net excludes birds from an airfield: implications for reducing bird strike and crop losses. Ecological Applications doi: 10.1890/15-0829.1.

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