image: Dan Mennill, the study's senior author, holds a nocturnal flight call microphone used to survey avian biodiversity during migration. view more
Credit: C. Sanders
It's not just lights on skyscrapers that can impact migrating birds--new research in The Condor: Ornithological Applications demonstrates that even ground-level artificial lights can affect birds passing overhead at night.
Most birds migrate at night, and artificial light disrupts migrations in a variety of ways, throwing off birds' natural navigation abilities and even attracting them to fatal collisions with buildings. The bulk of the research on how lights affect birds has been focused on lights on tall structures like skyscrapers and cell towers, but most artificial lights are actually near ground level--street lights, porch lights, and car headlights, to name just a few.
Matt Watson, David Wilson, and Daniel Mennill of the University of Windsor recorded the flight calls of migrating birds passing overhead during the 2013 fall migration in southern Ontario, Canada, comparing sites with and without ground-level artificial lights. Analyzing 352 hours of recordings, including the calls of at least 15 bird species, they found that significantly more flight calls were recorded at lit sites than at dark sites. "By pointing microphones at the night sky, we can survey migratory birds based on the quiet sounds they produce in flight," says Mennill. "This simple technique offers a special opportunity because we can resolve particular species of birds, or groups of species, using a fairly simple technology."
"It was exciting to find that even low-level anthropogenic lights affect call detections from migrating birds," adds Watson. Their findings have several possible explanations--ground-level lights could be disorienting birds, causing them to call more often and decrease their altitude as they attempt to straighten themselves out, or they could actually be attracting additional birds, as has already been documented with higher-elevation lights. In either case, artificial lights are causing migrating birds to waste energy, which could affect their chances of surviving their journey.
This study underscores importance of studying the consequences for wildlife when human activities alter the natural environment. "Anthropogenic light has profound effects on wild animals. For migratory birds, we know that lights on top of skyscrapers, communication towers, and lighthouses disorient and attract birds," says Mennill. "Our study reveals for the first time that even low-intensity lights on the ground influence the behavior of migratory birds overhead."
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"Anthropogenic light is associated with increased vocal activity by nocturnally migrating birds" will be available April 13, 2016, at http://www.aoucospubs.org/toc/cond/118/2.
About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society.