Tiny Hummingbirds’ Incredible Migration

AUK-15-160 B Dossman

Image credit: B. Dossman

Tiny Ruby-throated Hummingbirds are capable of flying more than 2,000 kilometers without a break, according to a new paper in The Auk: Ornithological Advances. This research provides some of the first details of their annual fall journey from the eastern United States to Central America, showing that their fall migration peaks in September and that older birds travel ahead of younger ones.

Collecting data on birds passing through southern Alabama, Theodore Zenzal of the University of Southern Mississippi and his colleagues found that hummingbirds moved through the area between late August and late October, with older birds arriving earlier and in better condition. Using a computer program to estimate flight range based on birds’ mass and wingspan, they estimated that the average hummingbird has a flight range of around 2,200 kilometers. Older birds and males were predicted to be able to travel farther at a time than younger birds and females.

These results suggest that older birds are more experienced and socially dominant, leaving their breeding territories earlier and traveling faster. Whether Ruby-throated Hummingbirds migrate across the Gulf of Mexico or around it is still unknown, but the flight ranges researchers calculated mean that most of them would be able to make it across if weather conditions were favorable. “The most interesting thing, in my opinion, is how some of these birds effectively double their body mass during migration and are still able to perform migratory flights, especially given some of the heftier birds seem to barely make it to a nearby branch after being released,” says Zenzal, whose work was funded in part by the National Geographic Society.

Zenzal and his colleagues captured hummingbirds with mist nets at Alabama’s Bon Secour National Wildlife Refuge during the fall migrations of 2010–14, banding and recording data on an amazing 2,729 individual hummingbirds. Even a visiting documentary crew was charmed by the tiny birds. “All but one person on the crew was from Europe and most had never seen a hummingbird in real life, so you can imagine how fascinating these birds must have seemed,” says Zenzal. “During the course of filming, members of the crew would regularly ask me to place a hummingbird in their hand so they could release it.”

“Patterns we previously had hints of from small, anecdotal observations are documented here with a very large sample size. It’s interesting that the young of the year migrate after adults and are quite different in their stopover phenology. This suggests there are substantial differences between flying south for the first time, as opposed to flying somewhere again as an adult,” says UC Riverside’s Chris Clark, an expert on hummingbird behavior. “I think that further research on how young hummingbirds migrate, and the decisions they make, would be really interesting.”

Stopover biology of Ruby-throated Hummingbirds (Archilochus colubris) during autumn migration is available at http://www.aoucospubs.org/doi/full/10.1642/AUK-15-160.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

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