FACTS RE THE AFFECTS OF LIGHT ON THE MIGRATORY BIRDS THAT FLY TO THE SEAFORD EDITHVALE WETLANDS
Birds have to use things to orient. One of the tools in their kit is celestial cues, so they can use the star maps like early navigators,” Susan Elbin, director of conservation and science at NYC Audubon, says. Believing they’re flying toward starlight or something similar, nocturnal migrants are drawn to the dazzling display, where they end up wasting crucial energy flying around and sounding off in distress.
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.
“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.”
Excessive or misdirected artificial light at night (ALAN) produces light pollution that influences several aspects of the biology and ecology of birds, including disruption of circadian rhythms and disorientation during flight. Many migrating birds traverse large expanses of land twice every year at night when ALAN illuminates the sky.