The bright lights emitted at night from bustling urban centers cause an unexpected evolutionary adaptation in some bird species. A recent study found that some birds living in smaller cities have the eyes of similar birds living far from such centers—a phenomenon that may hint at profound consequences of humanity's actions on its environment. We've used ChatGPT to keep your eyes open.
Researchers from Washington State University and Texas Agricultural and Mechanical University in San Antonio conducted an extensive study, focusing on San Antonio's bird population. They discovered an astonishing difference in eye size between two common songbirds – the Northern Cardinal (pictured) and the Carolina Gidron, which live year-round in the urban core of the city, compared to their counterparts living far from the city. The eyes of the city's birds were about 5% smaller, a fascinating evolutionary change that raised important questions about the impact of urbanization on wildlife.
The study, published in the journal Global Change Biology, found no similar difference in eye size for two migratory bird species—the painted hump and the white-eyed viroi—regardless of whether they were in the city center or on the outskirts of the city during the right season. Jennifer Phillips, a wildlife ecologist at Washington State University and senior author of the study, explained that birds "may adapt over time to urban areas, but migratory birds do not."
The reason, she says, lies in differences in exposure to 'light pollution' and noise; While native birds experience constant man-induced light and noise pressures, migratory birds spend the winter in areas with fewer sensory pollutants, making it difficult for them to adapt to the demands of city life during the breeding season.
The study's findings have significant implications for bird conservation, especially given the alarming decline in bird populations in the U.S. and Canada. Previous studies have shown the loss of 29% of the bird population, or 3 billion birds, since 1970, likely largely due to habitat fragmentation. However, this study suggests that sensory pollutants, such as artificial light, may also play a role in influencing bird behavior in urban environments.
Urban environments are characterized by constant artificial lighting, which can disrupt the natural rhythms and behaviors of birds. The study marks for the first time a link between urban light and bird eye size. Smaller eyes may be an evolutionary adaptation that allows these birds to better cope with the intense city lights. Larger eyes, on the other hand, increase the susceptibility to glare or sleep disturbances, causing birds a significant disadvantage.
Todd Jones, the study's first author and now a postdoctoral fellow at the Smithsonian Institution's Migratory Bird Center, emphasized that while humans do not intentionally affect birds, our actions have unintended consequences for them, requiring careful consideration.
Phillips is now leading a research team aimed at delving deeper into the impact of light and noise pollution on bird species, and has already received a $2.1 million grant from the National Science Foundation.
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