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Birds around airports may be deaf and more aggressive

Birds around airports are more aggressive and sing as if they have hearing loss. Collaboration between researchers of Manchester Metropolitan University and the Institute of Biology Leiden has led to surprising new findings about the impact of anthropogenic noise on birds around airports. Publication in Journal of Animal Ecology.

Associate professor Hans Slabbekoorn from the Institute of Biology Leiden is involved in the study that was recently published in the Journal of Animal Ecology. The study revealed that chiffchaffs (Phylloscopus collybita - see textframe) sing at lower frequencies when their territories are closer to the noisy runways at Manchester Airport or Amsterdam Schiphol Airport. The reason for this may be deafness at high frequencies due to the extreme exposures to airplane noise that happen every three minutes, throughout the day.

Chiffchaff on speaker (Javier Sierro)

Too loud

Earlier studies on great tits (Parus major), chiffchaffs and many other bird species have reported noise-dependent upward shifts in song frequency for a more moderate range of sound level variation along highways and in urban areas. The explanation for that finding was a potentially adaptive one: singing higher improves audibility by avoiding the low-frequency masking noise of traffic. Aircraft noise, in contrast, is so loud and covers all frequencies, that it does not allow such a benefit, no matter how the singing bird shifts to different song frequencies.

Angry birds

Experiments of birdsong played back at wild chiffchaffs also showed more aggressive responses by territorial males at the British airport compared to the quiet control area. According to the researchers this may be due to noise-induced physiological stress, disturbed communication, or some other unknown impact. Physical fights, instead of settling conflicts by song, drain energy from birds. In result, this energy will not be available for reproductive efforts and makes the birds more vulnerable to injury and predation.

Worldwide concern

The researchers think there is no reason to believe that these findings are confined to this particular study species or the specific research areas. Slabbekoorn: ‘Estimates by our team for the avifauna just around Manchester Airport within the noise exposure zone are that probably about 16.000 individuals of 100 species experience aircraft-related hearing loss. Considering that airports all over the world are still growing and spreading, this is a worldwide concern.’

Banner photo: chiffchaff near airport (Herman Berkhoudt)

Leiden roots and ties

Corresponding author of the article Selvino de Kort is a former student of Leiden University. He defended his PhD-thesis on ‘Pigeon pidgin’ in 2002 with Professor Carel ten Cate as promotor at the Institute of Biology Leiden. The current collaboration emerged trough old ties with IBL-researcher Hans Slabbekoorn, who served as advisor to the PhD-project at Manchester Metropolitan University of first author Andrew Wolfenden. Slabbekoorn also joined forces in this particular study by sending out IBL-students of the 2nd year field course to get recordings in wooded areas around Schiphol and Meijendel, as noisy replicate and quiet control area, respectively.   

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