While the bright city lights may be attractive to night owls of the human kind, they are known to be detrimental to migrating birds of the feathered variety. Now, new research has revealed that even artificial lights at ground-level can interfere with migratory birds flying overhead during the night.
Most birds undertake migratory flights at night, using the stars as a compass to guide them on their way. Artificial light sources can disrupt bird migration in a number of ways, disrupting their inherent navigation abilities or causing them to collide with buildings, often with fatal consequences.
Previously, most research focusing on the impact of artificial lighting on bird migrations has centered around tall structures such as cellphone towers, light-houses and skyscrapers, however, most artificial light sources are found closer to the ground — for example, street lights, vehicle headlights, porch and garden lights.
In a new study that was recently published in the scientific journal, The Condor: Ornithological Applications, a team of ornithologists from the University of Windsor recorded flight calls of migratory birds as they passed overhead on their flight through the Great Lakes, to the south of Ontario, Canada, during the fall migration of 2013. They compared sites that were lit up with artificial ground-level lighting to those where no ground-level artificial lighting was present.
After analyzing hundreds of hours of recorded in-flight calls of more than 15 different species of birds, the researchers found that the recordings taken at artificially lit sites showed significantly more in-flight calls than the recordings taken at darker sites where there was no artificial lighting.
Using this simple method of pointing microphones up towards the night sky, scientists are able to survey migrating birds by recording the barely audible sounds they make in flight, enabling them to identify different species or groups of bird species by the sounds they make.
The researchers found that sites lit up with low-level artificial lighting affected call recordings of the migrating birds passing overhead, with more call activity detected in light sites than dark sites. There could be several explanations for this — ground-level artificial lighting could be causing the birds to become disorientated, which in turn may cause them to drop down lower as they try to regain their bearings, and call more frequently to others in their group; or the lights may in fact be attracting other birds, which has been documented in studies conducted on the impacts of high-level lighting.
As more frequent calls equates to wasted energy, in both scenarios, artificial lighting is causing migratory birds to expend energy that could be used more effectively to improve their chance of survival. Migration takes its toll on birds physically, and any energy that is wasted could mean the difference between surviving the journey or not.
According to BirdLife International, 2000 bird species undertake regular seasonal migrations, some covering thousands of miles from their overwintering grounds to their breeding grounds. More than 40% of these migratory species are declining, with nearly 200 having a status of globally threatened.
This study highlights the importance of understanding the impacts that human activities that change the natural environment have on wildlife.
“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.”
Just another reason to turn all but the essential lights off at night, particularly lights outdoors. If you must have a security light on outside, rather opt for a motion-sensor light that turns on when a movement is detected. Light pollution not only impacts your neighbour, it impacts wildlife such as migrating birds, who may not survive their journey because of it.