A new study shows how quickly evolution can happen.
When the UCLA campus in Los Angeles was nearly empty during the pandemic, something remarkable changed in one permanent resident: the gray junco. The beak of these city birds became longer and slimmer in a short time. When students and employees returned, the beak shape changed again. The research can be found in Proceedings of the National Academy of Sciences.
Forest bird in the city
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The gray junco is a small songbird from the sparrow family. Normally it lives in forests. In Southern California, the species has now also established itself in cities and suburbs. There the gray junco searches for crumbs, snacks and other food that people leave behind. Researchers at UCLA have been tracking the juncos on campus for years. The lockdown suddenly showed them in real time how fast evolution can really go.
Professor of Ecology and Evolutionary Biology Pamela Yeh says: “We often think that evolution is slow, and most of the time it is. It was incredible to see evolution happening almost before our eyes, and to see so clearly the impact of humans on a living population.”
Longer and thinner
In the study, biologists describe how quickly that change occurred. During the closures, when there were few people on campus, young juncos gradually grew beaks that more closely resembled those of forest juncos: longer and thinner. Before the pandemic, researchers more often saw shorter, somewhat thicker beaks in urban birds. When campus life started again, that form immediately returned.
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Team member Eleanor Diamant was surprised by the strength of the effect. “We were honestly quite shocked to see how dramatic that change was,” she says. The researchers think there is a simple explanation behind it. On a normal day, juncos like to forage for food in places where people gather: squares, terraces at eateries and along busy walking routes. During the lockdown, that food source largely dried up. The gray juncos therefore had to get their food from somewhere else.
Territorial behavior
In such scenarios, other bird species are inclined to move to other places, but not the gray junco. Gray juncos are territorial birds: they defend their own area and stay there as long as possible. Moving to other places in the city with more food was therefore not an option during the lockdown. As a result, they were forced to make do with the food on campus themselves. The result: they started hunting for seeds hidden among leaves and bushes.
The researchers think this led to selection. A longer, slimmer beak may be better for picking seeds from plant material. Diamant: “We think that juncos with certain beak shapes were more successful when the campus was closed. Birds with beaks that were better for seed hunting probably had more food and had more young.”
Shorter snout
According to the team, the fact that the effect later reversed confirms that people really have something to do with it. As soon as the campus filled up again, the easy leftovers and the old beak shape returned. Yeh: “Wild animals have to work hard to find food. If people make that much easier, body parts that help with this, such as the mouth, can change along with it.”
The research fits into a larger picture: physical changes caused by living among people have also been reported in other urban animals. For example, previous research shows that some urban rats and raccoons have shorter snouts when they live in the city.
We have written about this subject before, for example also read: Little kestrel guards American cherries by chasing away snapping birds and Can birds imitate Star Wars robots? Yes, some even surprisingly good. Or read this article: Solar eclipse makes birds spontaneously sing as if it were morning.
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