City Birds Are Evolving To Be More Flexible and Assertive Than Their Country Cousins

Animals are adapting to life in the big city

Paul J. Hurtado

Humans aren’t the only ones who have to adjust to the pace of life in a big city. Animals do, too, and some are here for the long haul. New research finds that the dark-eyed junco, a common songbird, is evolving its behavior to better adapt to city life in San Diego.

Like their human counterparts, the urban juncos’ city lifestyle seems to make them more tolerant to crowds and hustle. Compared to juncos researchers sampled from rural locations, the city birds allowed scientists to approach closer before they took flight, were more willing to explore new habitats while in captivity and produced lower levels of stress hormones when the researchers handled them.

As Scienceline’s Kate Baggaley writes:

Urban life provides a constant barrage of stimuli, demanding that birds be more flexible when foraging and nesting. The differences between these populations in behavior and physiology suggest that, when it comes to city living, it’s better to be bold.

In the new urban environment, natural selection favored assertive birds. These braver juncos were more likely to pass on their genes, including those correlated with bold behavior and lower corticosterone levels. Over time, the authors propose, the population evolved and boldness became the norm. Similar changes are being observed elsewhere in America and Europe as other groups of urban birds become bolder.

The juncos, meanwhile, are reaping the benefits of their flexibility and brazenness in their urban home, often setting up nests in bike helmets and flowerpots, the researchers report.

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