Evolving to survive as the fittest is often portrayed as gradual, yet cases have been documented in which animals evolved within a century. Dark-eyed junco songbirds do not naturally live in urban areas, and mostly inhabit mountain forests. The climate crisis has driven them into cities, where they have made their residence in Southern California, including on the University of California, Los Angeles (UCLA) campus. This bird from the sparrow family is displaying an evolutionary turbocharge.
City-dwelling birds have shorter and stubbier beaks when compared to their forest-dwelling kins, whose beaks are longer to forage for nuts and seeds. However, UCLA researchers observed an unusual pattern in the beak shapes of city-dwelling birds hatched in 2021 and 2022, during the pandemic. They had longer beaks like their mountain counterparts. However, once pandemic restrictions were lifted, students returned to campus, and so did the shorter, stubbier beaks of juncos hatched in 2023 and 2024.
“We often think about evolution as a slow process,” said Eleanor Diamant, the study’s lead author who was a doctoral student at UCLA during the research and is now a visiting assistant professor at Bard College in Annandale-on-Hudson, New York.
“We thought that this would probably be too short of time to see a change in the population. … So we were really surprised when we ran the data,” Diamant added. “When I did the year-by-year comparison, it was remarkable how stark the change was.”
According to the authors, the city-dwelling juncos had shorter beaks to adapt to a broader range of diet of human food scraps. When classes went online and dining halls were closed in 2020, the birds had to resort to their natural diets, with newly hatched birds having longer beaks to feed on, as in forest-dwelling juncos. The study is a stark reminder of how anthropogenic factors significantly affect wildlife and how human activities influence the rate of evolution.
Diamant and Pamela Yeh, the study coauthor and a professor of ecology and evolutionary biology at UCLA, have pointed toward other recent examples of rapid evolution in birds, such as hummingbirds and great tit birds developing longer beaks. Factoring in the human angle of evolution and the shifts in daily activities that drove rapid evolution opens a new perspective into how evolution operates in the modern world.
Evolution is the primary hypothesis, although chances of gene flow are not being overlooked, in which mountain birds might have entered the urban population. The authors think this is not the case, as no behavioral changes were noticed. They are now working on collecting blood samples to gain genetic information and pinpoint if the changes in beak shape arose from genetic changes.
This is the first instance of rapid evolution that occured as a result of the pandemic, and that too, in two pulses, once into and then out of the pandemic condition. Yeh, who has been studying juncos for three decades, have long-term datasets on the birds. Keeping datasets is important because it keeps changes in features like beak shape tracked over a long time. Dark-eyed juncos are a declining species, which makes keeping records far more important for scientists to learn to protect them better.
Charles Darwin found evidence of his theory of evolution in finches in Galápagos off the coast of Ecuador. Later, a drought in the 1970s favored larger beaks in finches to feed in the harsh environment. Rapid evolution to adapt to the drought and to eat harder seeds drove natural selection, a process that passes down advantageous traits, and the birds over the next generations acquired larger beaks.
Evolution of juncos showcase how far our actions go in determining the traits an animal needs to survive. As our ideas, visions and technology evolve, we might have an even greater impact in how animals evolve. It is the right time to acknowledge the significance of our activities, and steer away from behavior that can adversely affect wildlife and make rapid evolution a necessity to not be endangered or extinct.
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