Alpine Swifts, Migrating Birds, Can Stay In Flight For 6 Months At A Time

By Josh Lieberman on October 9, 2013 4:03 PM EDT

alpine swift
Alpine swifts are capable of staying aloft for over 200 days at a time, Swiss researchers studying the birds' migration habits have found. (Photo: Wikimedia Commons)

Researchers in Switzerland say they were "totally blown away" last year when they discovered that Alpine swifts they were studying stayed in the air for six months straight. Scientists already knew that the Alpine swift, an eight-inch bird with a wingspan of about 22 inches, spent most of its life in flight, but no one realized the birds were able to spend this much time in the air without landing.

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Scientists from the Swiss Ornithological Institute and the Bern University of Applied Sciences in Burgdorf, Switzerland, attached electronic tags to a flock of six swifts to study their migration. The birds breed in Europe during the summer, migrating thousands of miles to West Africa when it gets cold. The researchers were looking to find out how often the Alpine swifts stop and how much energy was required for their long migration.

When they birds returned from West Africa after the winter, scientists checked out the tags of three of the swifts and found, much to their surprise, that the birds were in the air for every minute of their time in Africa -- over 200 days in the air without touching down. 

"It seemed to me unlikely that they did not rest somewhere on trees or cliffs," said ornithologist Felix Liechti, lead author of a study on the findings published in Nature. "I was very surprised."

The birds didn't have to touch down to eat during their migration. Instead, swifts can eat midair by feeding on aeroplankton (or arial plankton), bits of bacteria, fungus, insects and other little things that float on air currents. And it's unclear whether the birds sleep during midair, but stretches of less vigorous movement suggest they might be catching some rest here and there.

The electronic tags attached to the birds reported their acceleration patterns, recording when they were flapping their wings, gliding and resting. The tags only collected data every four minutes, so it's possible that the birds touched down in between readings. Every single piece of data, however, showed the birds either flying or gliding, so it would be somewhat unlikely for them to have stopped in the intervals between readings.

"We cannot rule out that the Alpine swifts may interrupt their flight for a few minutes," the team wrote in a study appearing in the journal Nature. "Nevertheless, they must be able to accomplish all vital physiological functions in flight over a period of several months."

A big unanswered question from the study, is not how the swifts are able to spend six months in the air, but why they would do so. 

"We can only speculate as to what the profit is of staying airborne all the time," Liechti said. "Is it avoiding predation? Parasites? We don't know."  

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