California’s Hummingbirds Have Changed Their Beaks in Response to Backyard Feeders, Study Finds
With plenty of artificial nectar available, Anna’s hummingbirds have expanded their range northward and their beaks have tended to become longer and larger
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Many bird enthusiasts like to hang bright red feeders filled with homemade sugar water to attract hummingbirds to their gardens. Now, new research suggests this common practice may be driving rapid evolutionary change in one species in California.
The beaks of Anna’s hummingbirds (Calypte anna) have gotten longer and larger over just a few generations, thanks largely to the proliferation of hummingbird feeders after World War II, according to the study published last week in the journal Global Change Biology. In addition, the growing popularity of hummingbird feeders has allowed the tiny birds to expand their range northward, from Southern California all the way up the coast to British Columbia.
To understand how Anna’s hummingbirds have changed, scientists gathered and analyzed data from a variety of sources. They scoured California newspaper archives for hummingbird feeder advertisements between 1860 and 2020, as well as information about the spread of eucalyptus trees—a year-round, non-native source of nectar.
They also collected data from the Audubon Christmas Bird Count, an annual citizen science survey that helped them map the species’ range between 1938 and 2019. Data from the U.S. Census helped them plot human population density over the same period.
Finally, the team measured the beaks of 400 Anna’s hummingbirds in museum collections that span the years 1861 to 2020, to see how they had changed over time.
“We did really cool shape analyses, we looked at all the shapes of beaks in two dimensions as well as three dimensions,” says study lead author Nicolas Alexandre, a geneticist now with Colossal Biosciences who conducted the research while at the University of California, Berkeley, to SFGate’s Kasia Pawlowska.
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Together, their analyses paint a picture of how human activities have shaped the Anna’s hummingbird over time. First, the widespread planting of eucalyptus trees starting in the mid-1800s seems to have allowed the petite birds to begin expanding their range.
But once hummingbird feeders took off, the birds really began to thrive. Their range continued to grow, and their bodies adapted to the artificial abundance of food. In areas where feeders were common, the hummingbirds’ beaks got bigger—which is the equivalent of “having a large spoon to eat with,” says study co-author Alejandro Rico-Guevara, an evolutionary biologist at the University of Washington, to Science’s Rachel Nuwer. Male birds in these areas also developed sharper, pointier beaks compared to females, a territorial adaptation that probably helped them fend off competing males.
“Imagine you have a bunch of flowers, and the shape of the flower is going to constrain how efficiently you can feed from that flower. Now imagine you have this giant reservoir of nectar that’s always available,” says Alexandre to the Guardian’s Cy Neff. “I want to get as much nectar with every drink before someone displaces me at the feeder. A longer beak with more volume is going to be advantageous.”
The beaks of birds living in colder regions, however, got smaller and shorter. This change likely helped these Anna’s hummingbirds conserve heat, since their beaks help with thermoregulation, as the team showed with an infrared camera.
California’s Anna’s hummingbirds adapted relatively quickly. Researchers saw changes over the course of just about ten generations. Though we often think of evolution as happening slowly, over hundreds of thousands or even millions of years, it can—and often does—occur “literally in front of our eyes,” Rico-Guevara tells NPR’s Kat Lonsdorf.
“And we just need to pay attention to it,” he adds.
But while the Anna’s hummingbird has successfully adapted to urbanization, other hummingbird species have “sharply declined” alongside the same human influences, writes Elizabeth M. Steell, an evolutionary biologist at the University of Cambridge in England who was not involved with the research, in a commentary accompanying the study.
Why is that? It’s not entirely clear, but Steell suspects the Anna’s hummingbird may have a “high propensity” for evolving its physical features when faced with human-driven changes to its environment. Future research might be able to shed more light on what makes the Anna’s hummingbird so flexible, she adds.
Anna’s hummingbirds are far from the first species to adapt to human-caused changes to their environment. In fact, Alexandre was initially inspired to conduct the study after learning about how seed feeders in the United Kingdom may have caused the beaks of great tits to grow longer than their counterparts in the Netherlands.
Ivory poaching in Mozambique led to a rise in tuskless elephants, while peppered moths became darker in response to air pollution during the Industrial Revolution. Pigeons also adapted in response to human development, nesting on skyscrapers instead of on cliff faces and expanding their range alongside people.
And these are just a few examples. Scientists think they’re “going to find more and more examples of contemporary and subtle changes… that we’re shaping, indirectly, in many more species,” says Roslyn Dakin, an animal behaviorist at Carleton University in Canada who was not involved with the new research, to Science.
