Covid-19 ‘anthropause’ altered beak shape of urban birds: Study

The anthorpause that followed the Covid-19 pandemic disrupted social behaviours. Scientists have now reported that such a prolonged stoppage of human activities has also led to birds changing their physical appearance, which may be due to an “adaptive sensitivity".

For decades, dark-eyed junco, a forest-dwelling sparrow, inhabited Los Angeles, including the sprawling campus of the University of California. The beaks of the city-dwelling birds are little different from their wild land counterparts. Urban juncos have shorter, thicker beaks, possibly due to differences in their diets. In addition to their natural food sources, the birds living on the UCLA campus also consume substantial amounts of food waste left by students since the pandemic began. The classes moved online, and the campus became empty.

Scientists in the Department of Ecology and Evolutionary Biology were monitoring juncos as part of their long-term study of breeding behaviours. They observed that birds hatched during the pandemic-related restriction period had beak shapes and sizes different from those of birds hatched before and after the restriction-related pause in human activity.

Birds born during the pandemic period had beaks similar to those of forest-dwelling species. The juncos born in 2021 and 2022 had longer, slimmer beaks that are more atypical of wild land species. But birds born after the pandemic, when students returned to the campus, had the same old short beaks. While the cause of such a rapid shift in bill morphology remains unclear, the findings suggest high adaptive sensitivity in an urban bird population to the cessation and resumption of human activity.

"We speculate that food waste may drive the adaptive evolution of a more generalist bill shape in urban juncos, which rapidly shifts at a population level in response to resource change. Future work should determine how bill shape varies with foraging, fitness, and genetics in juncos,” UCLA scientists Pamela Yeh and Eleanor Diamant reported in the Proceedings of the National Academy of Sciences.

There may be other factors, such as the urban environment, as foraging on hard surfaces may have contributed to shortening the bill. The scientists said Covid-19-induced restrictions provided them with an opportunity to test the extent to which human activities affect other species. Earlier, it was observed that other birds reduced the volume of their songs in the absence of human activity.