A staggering event on October 4-5 in Chicago led to the demise of nearly 1,000 birds, as they crashed into a brightly lit glass structure. While such extensive bird fatalities are uncommon, artificial light remains a significant and escalating hazard to migratory birds.
In a comprehensive study published in Nature Communications, researchers employed weather radar data to chart bird stopover densities across the U.S. The study revealed that artificial light is a prime factor influencing where birds land during migration.
Kyle Horton, an assistant professor at Colorado State University’s Department of Fish, Wildlife and Conservation Biology and the study’s lead author, explained that city lights can entice birds into hazardous urban environments.
The challenges for migrating birds in urban areas are manifold, including dangerous building collisions, habitat loss, limited food availability, and threats from humans and predators like cats. Urban parks offer some respite, but they come with their own set of challenges, such as competition for scarce resources.
Migration is fraught with peril for birds, involving extensive travel that can deplete up to half of their body mass. “These stopover locations are the fueling stations,” Horton said. “If they don’t have a good spot to rebuild energy supplies, migration can’t happen.”
This study marks the first time migration stopover hotspots across the contiguous United States have been mapped on such a large scale. Understanding these patterns can aid in developing conservation strategies.
“Cities pose multiple risks to migrating birds,” explained co-author and Michigan State University Professor Geoff Henebry. “They also offer resources for the tired birds to rest and refuel.”
“Our study is notable in that it combines big data – and a lot of processing – from the weather surveillance radar network with big data from multiple spaceborne sensors to address key questions regarding the influence of urban areas on bird migration.”
However, the attraction of birds to cities raises a conservation dilemma: should urban areas be preserved as vital stopover sites, or should efforts be concentrated on reducing urban lighting? Horton is collaborating with various organizations to tackle both issues, but the multifaceted nature of urban lighting presents complexities.
Light pollution not only affects birds but also disrupts human circadian rhythms, contributing to several health issues. “We don’t often think about light as a pollutant, but it checks all the boxes of what pollution is,” Horton said.
Initiatives like BirdCast offer migration forecasts and real-time maps, enabling individuals and cities to minimize artificial light on critical migration nights. Simple measures, such as retrofitting windows with decals and adjusting light brightness and color, can significantly reduce bird collisions.
The tragic incident at Chicago’s McCormick Place Convention Center is a stark reminder of the dangers of light pollution. Public awareness and simple actions, like turning off unnecessary lights, can have an immediate and beneficial impact on bird safety.
“If we turned off all lights tonight, there would be no birds colliding because of lights tonight,” Horton concluded.
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