Eyes of birds are growing smaller because of light pollution from cities | Science News

A northern red cardinal, one of the birds affected by light pollution. (Image Credit: Joshua J Cotten/Unsplash).

A new study indicates that the light pollution from major cities could be causing birds to adapt, by reducing the sizes of their eyes. The researchers investigated two common songbirds that live around San Antonio, Texas, USA, the Northern Cardinal and the California Wren. The researchers were able to determine that the birds that lived closer to the city centre had five per cent smaller eyes than the birds that lived in the outskirts. However, researchers found no differences in the eye sizes of two migratory species, the Painted Bunting and the White-eyed Vireo.

Previous research has indicated that the US and Canada has lost around 29 per cent of their bird population, amounting to three billion birds since the 1970s. According to the conventional understanding, the decline in bird population is because of habitat fragmentation. The new study indicates that sensory pollutants such as light pollution from human cities can be a contributing factor. The research is expected to inform conservation efforts. A paper describing the findings has been published in Global Change Biology.

Senior author of the paper, Jennifer Phillips says, “This study shows that residential birds may adapt over time to urban areas, but migratory birds are not adapting, probably because where they spend the winter—they are less likely to have the same human-caused light and noise pressures. It may make it more difficult for them to adjust to city life during the breeding season.”

Also Read | Scientists investigate link between temperature and sizes of bird body parts

The researchers also discovered that the centres of cities were less desirable for birds. Previous studies have investigated how light pollution in cities influence the timings of the dawn songs of birds, as well as their circadian rhythms, but this is the first study to investigate adaptations in eye sizes. The smaller eyes can help the birds adjust to the more intense light in city centres.

Also Read | Scientists investigate impact of marine heatwaves on apex ocean predators