Using a Sound Field to Reduce the Risks of Bird-Strike: An Experimental Approach

Each year, billions of birds collide with large human-made structures, such as building, towers, and turbines, causing substantial mortality. Such bird-strike, which is projected to increase, poses risks to populations of birds and causes significant economic costs to many industries. Mitigation technologies have been deployed in an attempt to reduce bird-strike, but have been met with limited success. One reason for bird-strike may be that birds fail to pay adequate attention to the space directly in front of them when in level, cruising flight. A warning signal projected in front of a potential strike surface might attract visual attention and reduce the risks of collision. We tested this idea in captive zebra finches (Taeniopygia guttata) that were trained to fly down a long corridor and through an open wooden frame. Once birds were trained, they each experienced three treatments at unpredictable times and in a randomized order: a loud sound field projected immediately in front of the open wooden frame; a mist net (i.e., a benign strike surface) placed inside the wooden frame; and both the loud sound and the mist net. We found that birds slowed their flight approximately 20% more when the sound field was projected in front of the mist net compared with when the mist net was presented alone. This reduction in velocity would equate to a substantial reduction in the force of any collision. In addition to slowing down, birds increased the angle of attack of their body and tail, potentially allowing for more maneuverable flight. Concomitantly, the only cases where birds avoided the mist net occurred in the sound-augmented treatment. Interestingly, the sound field by itself did not demonstrably alter flight. Although our study was conducted in a limited setting, the alterations of flight associated with our sound field has implications for reducing bird-strike in nature and we encourage researchers to test our ideas in field trials.