SCIENCE: Bird feeders have caused a dramatic evolution of California hummingbirds

 If you have a hummingbird feeder, here's a story you'll find interesting. Since their introduction, the feeders have been affecting the evolution in California hummingbirds. 

(Photo: Anna’s Hummingbird. Credit: USDA) 

Bird feeders have caused a dramatic evolution of California hummingbirds

Beaks have grown longer and larger, and ranges have expanded to follow the feeders 

21 May 2025 ByRachel Nuwer, SCIENCE 

Hummingbird feeders are a beloved pastime for millions of backyard birders and a convenient dining spot for the birds. But for the Anna’s hummingbird, a common species in the western United States, feeders have become a major evolutionary force. 

According to research published this week in Global Change Biology, artificial feeders have allowed the birds to expand their range out of Southern California up to the state’s northern end. They have also driven a transformation of the birds themselves. Over just a few generations, their beaks have dramatically changed in size and shape.

“They seem to be moving where we go and changing quite rapidly to succeed in their new environments,” says co–lead author Nicolas Alexandre, who conducted the work when he was a graduate student at the University of California, Berkeley and is now a geneticist at Colossal Biosciences, a biotechnology company based in Dallas. “We can think of Anna’s hummingbird as a commensal species, similar to pigeons.”

Carleton University animal behaviorist Roslyn Dakin, who wasn’t involved with the study, adds that the new paper beautifully shows “evolution in action.”

It’s unclear when the earliest hummingbird feeders appeared. A 1928 National Geographic article provided instructions for DIY feeders to observe hummingbirds, but the technology likely existed earlier. What is clear, though, is that hummingbird feeders took off after World War II. When Alexandre and his colleagues mined the text of newspaper archives dating back to 1880, they found that ads for feeders proliferated after the first patented one appeared in 1947.

To test how Anna’s hummingbirds responded to the uptick in feeders, the researchers turned to the Audubon Christmas Bird Count, an annual birding survey. Data from the survey showed which of California’s 58 counties the bird inhabited from 1938 to 2019. U.S. Census records indicated human population density in these same areas, while newspaper ads for feeders served as a proxy for feeder density. In addition, the team analyzed hummingbird museum specimens in 2D and 3D to quantify changes to their beaks over time. Finally, they built a model for predicting hummingbird range expansion that incorporated not just artificial feeders, but also other factors, including the locations of introduced eucalyptus trees, which can provide nectar throughout the year.

The researchers’ findings suggest eucalyptus trees—which were planted en masse in California in the late 1800s—might have served as the first steppingstone for some populations of Anna’s hummingbirds to expand their ranges. But hummingbird feeders played the biggest role in driving the hummingbird’s northward population growth. “The feeders are what really make the difference here,” says senior author Alejandro Rico-Guevara, an evolutionary biologist at the University of Washington. 

The researchers also found that as feeders proliferated, Anna’s hummingbird beaks got longer and larger, which may reflect an adaptation to slurp up far more nectar than flowers can naturally provide. Developing a bigger beak to access feeders “is like having a large spoon to eat with,” Rico-Guevara says.

This change was more pronounced in areas where feeders were dense. 

But in birds that lived in colder regions north of the species’ historical range, the researchers spotted the opposite trend: Their beaks became shorter and smaller. This finding also makes sense: The researchers used an infrared camera to show for the first time that hummingbirds use their beaks to thermoregulate, by dissipating heat while they are perched. A smaller beak has less surface area—and would therefore help conserve heat.

It wasn’t just the size and shape of beaks that changed. In areas where feeders are dense, male hummingbirds have also developed beaks that are pointier and sharper than usual. Pointy beaks in hummingbird species often indicate aggressiveness, and the researchers think male skirmishes over feeder control may have made these birds feistier. “Anyone who has a feeder knows that hummingbirds fight like crazy,” Rico-Guevara says.

The most surprising finding, though, was how quickly these changes took place. By the 1950s, hummingbirds were noticeably different from those of the 1930s: a time span of only about 10 generations of birds, Alexandre says.

Dakin says the study adds nuance to our conception of humans as an evolutionary force. Often, researchers think of humans as exerting selective pressures through environmental damage or deliberate domestication. But as with Anna’s hummingbird, “I think we’re going to find more and more examples of contemporary and subtle changes,” she says, “that we’re shaping, indirectly, in many more species.”