In a recent paper published in the Proceedings of the National Academy of Sciences, scientists reported that during and after the pandemic, dark-eyed juncos experienced two quick evolutionary changes. In particular, the beaks of little songbirds grew longer during the pandemic and then became thicker once again when human activity resumed, just like in the movie, pinocchioBut in this case, there was no magic or morality involved about honesty – only the consequences of human impact on nature,
“We have this idea of evolution being slow because, in general, over evolutionary time, it is slow,” Pamela Yeh, one of the study’s lead authors and an evolutionary biologist at the University of California, Los Angeles (UCLA), said in a statement. “But it is amazing to see evolution happening before our eyes and to see the obvious human impact changing a living population.”
easy means small
Black-eyed juncos typically live in mountainous forests, but in Southern California, climate change caused a large population of the birds to move into cities, where they learned to pick up bits and scraps from human food waste. Compared to their mountain relatives, Californian juncos’ bills tended to be shorter and thicker.
“Wild animals have to work hard to find and get their food. When humans make it so easy, the parts of their bodies, such as their mouth, that animals use to find food adapt,” Yeh said.
So when Jankosz settled in well on UCLA’s campus, he caught the attention of Yeh and his colleagues, who began a long-term study of the songbirds in 2018. Amazingly, the birds gradually evolved a diet “closer to that of the average college student,” the study’s other lead author and Bard College evolutionary biologist Eli Diament told The New York Times. So this included “things like cookies, bread…” [and] Pizza,’” he remembered.
hard means long
Then the pandemic came. As classes shifted online, the campus became mostly abandoned and scrap-free – causing significant losses to Junco. It was around 2021, about a year after the start of the pandemic, that Ye and Diamant noticed a slight change in the newborns: a longer, thinner beak.
“To be honest, we were quite surprised when we saw how strong that change was,” Diament recalled. In such a short time, California juncos had essentially “evolved” so that their bills returned to the size held by their counterparts in the wild. That change is likely to increase the birds’ foraging success rate, Diamant said.
But as pandemic restrictions eased, UCLA students, faculty and staff returned to campus. Remarkably, as people returned, the shape of the juncos’ beaks also changed. As the beaks grew, they shrank again in junco chicks born between 2023 and 2024.
“This is remarkable evidence of the rapid ability of these birds to adapt to changes in their environment and food resources,” biologist Graciela Gómez Nicola of the Complutense University of Madrid, who was not involved in the study, told Science Media Center Spain.
a gray area
Other recent studies have examined how exposure to human activity has changed the morphology of wild animals. But the researchers explained that juncos are somewhat different from other urban birds like house sparrows or pigeons. House sparrows and pigeons are “in some ways pre-adapted to live with people” due to their general diet, flocking tendencies, and ability to nest in human structures.
In contrast, juncos are territorial and usually nest on the ground. So the researchers concluded that UCLA’s dark-eyed juncos, whether they are common on campus, represent an ongoing evolutionary mystery.
“When we think about how human behavior impacts wildlife, I don’t feel like we have a lot of success stories,” Yeh said. “I wouldn’t quite call it a success story yet, but it’s not a disaster story, and that’s no small thing.”
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