Older hummingbirds better prepared

Lengthy annual migration reveals profound differences between young birds and the more experienced ones

The small, but mighty ruby-throated hummingbird flies 2,000 km on its migratory journeys without a break, researchers report in the journal The Auk: Ornithological Advances.

New research provides some of the first details of the hummingbird’s annual fall journey from the eastern United States to Central America. It shows that their fall migration peaks in September and that older birds travel ahead of younger ones.

The more experienced birds leave earlier and in better condition. They can fly farther and arrive sooner at their wintering grounds.

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“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,” said University of California-Riverside’s Chris Clark, an expert on hummingbird behaviour. “I think that further research on how young hummingbirds migrate, and the decisions they make, would be really interesting.”

While examining the birds’ annual fall journey from the eastern United States to Central America, the researchers also found fall migration peaks in September and that many of the birds are capable of flying more than 2,000 kms without a stop.

Theodore Zenzal of the University of Southern Mississippi and his colleagues captured ruby-throated hummingbirds with mist nets at Alabama’s Bon Secour National Wildlife Refuge during the fall migrations of 2010-14, banding and recording data on 2,729 individual hummingbirds.

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 kilometres. Older birds and males were predicted to be able to travel farther at a time than younger birds and females. They discovered the migration passes through the area between late August and late October.

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 favourable.

“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,” said Zenzal.

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