The Bright Burn of City Lights May Be Shrinking Bird’s Eyes: Study

A new study suggests that the bright lights of the city may be making birds' eyes smaller.

According to the findings, published in Global Change Biology, the northern cardinal and Carolina wren which reside in the urban center of San Antonio, Texas, have eyes approximately 5% smaller than members of the same species that live outside of the city.

Senior author Jennifer Phillips, a wildlife ecologist at Washington State University, explains that the "study shows that residential birds may adapt over time to urban areas, but migratory birds are not adapting."

This difficulty to adjust is believed to be caused by the fact migratory birds spend their winters in areas that don't have human-caused light and noise pressures.

"It may make it more difficult for them to adjust to city life during the breeding season," says Phillips.

For this study, the research team observed more than 500 birds from central and edge areas of San Antonio. They compared the body and eye sizes of the birds while analyzing noise and light measurements in each area.

According to Phillips, the smaller eye size may enable birds to deal with brighter and more constant light.