A hummingbird looks f or a meal among blooming rhododendrons at Hendricks Park in Eugene. The park covers over 80 acres and includes a rhododendron garden, paths and 200 year-old Douglas fir trees.
San Diego, California – Hummingbirds in California are changing—fast. Over the past century, and possibly in just a few decades, Anna’s Hummingbirds (Calypte anna) have developed sharper, pointier beaks, a rapid evolution scientists link closely to human influence.
Researchers studying historical bird data from 1938 to 2019 found that these tiny birds have dramatically expanded their range. Once limited mainly to southern California and Baja California in Mexico, Anna’s Hummingbirds now live as far north as southern Alaska. Two key human-driven changes seem to explain this shift: the widespread planting of eucalyptus trees and the growing popularity of backyard hummingbird feeders.
Eucalyptus trees, imported from Australia in the 1800s, and nectar feeders introduced in the 20th century provided the birds with a reliable, year-round food source. What was once a seasonal scarcity of nectar transformed into constant abundance, enabling hummingbirds to thrive far beyond their historical limits.
Along with the population growth and range expansion, the birds’ beaks have changed shape significantly. Museum specimens reveal that the hummingbirds’ beaks have become longer, sharper, and more streamlined in southern California. This evolution is likely an adaptation that helps them better access nectar from feeders and gives them an edge in territorial battles over feeding sites—fierce skirmishes that backyard birders are all too familiar with.
But there’s more to these elongated beaks than just feeding advantages. Infrared imaging shows that hummingbirds use their beaks to dissipate heat, similar to how elephants cool down through their ears. Their rapid wing beats and fast metabolisms need this natural cooling system. Interestingly, their beaks are shorter and stubbier in colder northern regions where the birds have more recently settled, probably to conserve body heat.
The pace of this evolution surprises scientists the most. Nicolas Alexandre, a geneticist who led the research, noted that the most dramatic beak changes occurred between the 1930s and 1950s—about 10 hummingbird generations. This rapid change challenges the idea that evolution is always slow, showing how human activity can quickly reshape wildlife.
The study, published in Global Change Biology, highlights how seemingly small human actions, like planting trees or setting out feeders, can profoundly affect nature. As senior author Alejandro Rico-Guevara explains, “The feeders are what really make the difference here.”
This discovery adds a new layer to understanding how humans influence evolution—not just through harm or domestication but through subtle ecosystem changes. As researchers continue to study these shifts, Anna’s Hummingbirds remind us that nature always adapts, sometimes in surprising and swift ways.
