Swifts Spend Nearly a Year on the Wing

The tiny birds spend about ten months of the year in the air almost without a break

A common swift in flight. Markus Tallroth

Not content with being one of the fastest animals on the planet, the common swift has just nabbed itself another title. According to a new study published in the journal Current Biology, the tiny birds are also some of the strongest fliers the Earth’s skies have ever seen, sometimes spending as much as ten months of the year aloft.

“It’s amazing,” Anders Hedenström, an ecologist at Sweden’s Lund University tells Hannah Devlin for The Guardian. “We knew they were extremely well-adapted to flight. They have very long and narrow wings and a streamlined body. They’re like Formula One cars or greyhounds.”

Considering that the little birds regularly migrate back-and-forth between Europe and sub-Saharan Africa, scientists have long suspected that swifts spend enormous amounts of time in the air. Swifts often weigh only a little more than an ounce, however, making data gathering tricky. In order to track the swifts’ flight patterns, Hedenström and his colleagues equipped 19 of these teeny fliers with lightweight devices that tracked how fast they flew, how high, where and the time of day, Merrit Kennedy reports for NPR.

In 2013 and 2014, Hedenström’s team snagged 19 swifts as they started their southbound migration from Sweden and hooked them up with the little loggers. When the researchers eventually caught up with the birds, they were shocked to see how rarely the swifts left the skies, James Gorman reports for The New York Times.

“They feed in the air, they mate in the air, they get nest material in the air,” Lund University researcher Susanne Åkesson tells Ed Yong for National Geographic. “They can land on nest boxes, branches, or houses, but they can’t really land on the ground.”

That’s because of the way their little bodies are shaped: they are optimized for flying and gliding over long distances and remarkable lengths of time, not for frequent takeoffs and landings. Not every swift stayed aloft the entire time, but even the ones that roosted more often flew much further than the vast majority of other birds, Devlin reports. The researchers even suspect that some swifts may not even land to take a snooze.

“That’s just a guess,” Hedenström tells Devlin. “From a human perspective it would be easier to take a nap when gliding when you wouldn’t be disturbed by flapping your wings.”

If so, they wouldn’t be the only birds with that ability. Earlier this summer, ornithologists studying ocean-spanning frigate birds found that the large seabirds sleep mid-flight, Yong reports. But this is a tough thing to study with swifts. It would take a much smaller brain sensor than any engineer has yet made to to collect similar readings for swifts as done with the larger frigate birds. But considering that sensors small enough to track the swifts in flight were almost unthinkable ten years ago, the answer may not be far off.

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