by Light pollution has steadily intensified and expanded from urban areas and, with the advent of LED lighting, is growing in North America by up to 10% annually, as measured by the visibility of stars in the night sky. In our recent study, we found that the brightness of cities and urban outskirts can powerfully attract migratory birds, drawing them to developed areas where food is scarcer and they face threats such as colliding with glass buildings.
Every spring and fall, migratory birds travel to or from their breeding grounds, sometimes traveling thousands of miles. Along the way, most birds need to make stops to rest and feed. Some species burn half their body mass during migration.
Stopover sites are not random and birds often use the same locations from year to year. Because migration occurs on a continental scale, with billions of birds crossing North America each migratory season, it is important for scientists to understand what attracts birds to these places.
We found that light pollution was one of the main predictors of migratory bird density at stopover sites during spring and fall migration across the continental US.
Because it is important
Almost all North American birds (about 80%) migrate each spring and fall. And of those species that migrate, 70% do so at night.
Nocturnal migration has many adaptive benefits: for example, weather conditions are better and there are fewer active predators. But it makes most migratory birds very susceptible to light pollution. In North America alone, it is estimated that up to one billion migratory birds die each year from collisions with buildings.
Scientists still don’t know why nocturnal migratory birds are attracted to artificial light, but research has shown that light pollution acts as an amplifying agent that attracts more songbirds to built-up areas. It often coexists with other environmental threats, such as water and air pollution and noise. All of these stressors alter the birds’ physiological and behavioral processes during already extremely exhausting journeys.
Lighting is part of the fabric of human structures, yet many people do not consider it a pollutant or perceive its harmful effects on nature, until events such as the mass loss of birds in Chicago on October 4 and 5, 2023, when Nearly 1,000 birds died after colliding with the McCormick Place Convention Center, making the problem impossible to ignore.
How we did our job
With colleagues from Colorado State University, Michigan State University, the University of Delaware, the Cornell Laboratory of Ornithology, Princeton University, the University of Massachusetts Amherst, and the National Park Service, we seek to understand the complex factors and large-scale patterns of scales. density by combining remote sensing data with geospatial tools. Mapping stopover sites has been a priority for bird conservation for many years; Now, for the first time, we have a complete view of where these stops are located in the United States.
We were able to create novel continental-scale maps using NEXRAD weather monitoring data from the US – information from the same radars that meteorologists use to predict weather patterns on TV and weather apps. We created 2,500 models using approximately 1 million locations in the US and 49 predictor variables, including forest cover, precipitation, temperature, elevation, and sky brightness (diffuse brightness in the night sky due to artificial light ).
These maps capture fine-scale details that allow us to see greater densities of migratory birds following the winding banks of the Mississippi River, which provide important refuge for exhausted migrants to rest and refuel. We also created fall and spring hotspot maps that highlight regions where especially high numbers of birds stopped over.
We found that the presence of light pollution was a better predictor of bird density than temperature, precipitation, or canopy cover. These were all variables that we expected to correlate with periods when birds would be on the ground, or with high-quality habitats where birds would likely stop.
Other variables were associated with areas that birds were unlikely to use as stopovers. An example was the presence of agricultural crops, such as corn or soybeans. Fields planted with a single crop do not provide adequate food or shelter for many bird species, so migrants are unlikely to rest there.
Light pollution is a human-induced change in the environment that can act as an ecological trap, attracting birds to poor habitats and increasing their risk of collisions with buildings. Fortunately, its immediate effects can be quickly reversed with the flip of a switch.
Working to reduce artificial light through Lights Out campaigns and migration alerts, understanding when birds will be in airspaces, and using bird-friendly glass that has patterns on its surface to make it more visible to birds will reduce bird deaths. birds due to light pollution. Understanding the drivers and macroscale patterns of scale densities across the continental US will better inform conservation actions like these.
The Research Brief is a brief version of an interesting academic work.
This article is republished from The Conversation, an independent, nonprofit news organization bringing you data and analysis to help you understand our complex world.
It was written by: Carolyn S. Burt, Colorado State University and Kyle Horton, Colorado State University.
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Kyle Horton receives funding from the National Science Foundation and the National Aeronautics and Space Administration.
Carolyn S. Burt does not work for, consult with, own shares in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond her academic appointment.
