Anna’s Hummingbird Beaks Have Evolved Due to Increasing Bird Feeders
- Jul 1
- 2 min read
Student Summary By Olivia Hwang
Original Source: Maddie Burakoff, Audubon, May 29, 2025
Abstract
Background:
Anna’s Hummingbirds were historically found only in a small range of chaparral habitat in southern California and northern Mexico, where the mild climate let them feed on nectar year-round. However, with the recent commercialization of hummingbird feeders, Anna’s Hummingbirds have been found to adapt in curious ways.
Objective:
Researchers sought to investigate the specific effects that hummingbird feeders have had on Anna’s Hummingbirds through recent generations.
Method:
To accomplish this task, researchers analyzed hundreds of preserved museum hummingbirds dating back to 1861, measuring their beaks. Because there were no direct records of how feeders spread, the team
counted historic newspaper advertisements for feeders, county by county, as a stand-in for feeder density, and used 80 years of Christmas Bird Count data to track the birds’ spread. They then compared these trends with the rise of feeders over time.
Results:
Researchers found that Anna’s Hummingbirds developed longer, more tapered beaks that could hold a larger volume of liquid. They reasoned that feeders didn’t require a delicate beak shaped to fit specific flowers; instead, the birds shifted toward scooping up more nectar with every gulp. This opposed previous nectar sources, such as manzanita or gooseberry blossoms, that required a more precise fit. Moreover, the study found that male Anna’s Hummingbirds developed sharper beaks, which they use as weapons to defend their feeders and territory. Finally, a deeper investigation revealed that feeder density showed the strongest relationship with the expansion of the Anna’s Hummingbird’s range. Notably, these changes happened quickly – within about two decades, or roughly 10 generations.
Conclusion:
This study allowed researchers to understand a case of human impact on wildlife. Even though this change was not necessarily negative, it raises questions about the future impacts of humans on the species we share our environment with. (Note: because the study did not analyze the birds’ genes, the authors describe these as shifts in traits over time that suggest feeders are shaping the species, rather than confirmed genetic evolution.)
