Artificial lighting in and around cities alters the cues migratory birds use to navigate and affects their ability to refuel during long journeys. Studies by Jeffrey Buler University of Delaware using radar and observational data link artificial light at night to behavioral attraction and disorientation in nocturnally migrating birds. Research by Travis Longcore and Catherine Rich Urban Wildlands Group framed this phenomenon as ecological light pollution, showing how skyward lighting creates extended skyglow that changes the visual environment birds rely on.
How lighting disrupts navigation
Many migratory species navigate using stars, the moon, and geomagnetic cues. Bright urban lighting masks celestial cues and creates bright gradients that draw birds toward lit areas. Kevin J. Gaston University of Exeter has emphasized that the spectral composition of light matters because shorter blue-rich wavelengths scatter more and can be more attractive to some species. Christopher C. Kyba GFZ German Research Centre for Geosciences has documented how urban skyglow extends far beyond city boundaries, meaning coastal and rural stopover sites can be affected even when they appear dark to people.
Effects on stopover success and survival
Attracted birds often end up in urban centers where collisions with buildings and towers increase collision mortality, a primary documented cause of death for migratory passerines in many regions. Jeffrey Buler University of Delaware found that disoriented flocks can spend energy circling lit areas, reducing fat reserves needed for onward migration and lowering stopover success. Light-altered behavior can also change where birds choose to land, occasionally pushing them into suboptimal habitats with higher predation risk or lower food availability, which has population-level consequences for species already stressed by habitat loss.
Urban lighting therefore interacts with human cultural and territorial practices. Seasonal events, sporting venues, and architectural lighting patterns can create temporal spikes in risk, while coastal and inland flyways experience different exposure depending on urban layout and prevailing weather. Mitigation strategies emerging from research include timed dimming, shielding, and changing light spectra to longer wavelengths, measures supported by multiple studies as ways to reduce attraction and collision without compromising safety. Not all species respond the same, so locally informed policies that combine monitoring with targeted light management are most effective for conserving migratory bird populations.