Alpine Swift
The Alpine swift stays aloft for 200 days while migrating between Africa and Europe, a study has found. (Daniele Occhiato / August 29, 2010)
October 8, 2013, 2:29 p.m.
Talk about a red-eye flight! After attaching electronic monitors to half a dozen Alpine swifts, researchers say they were shocked to discover that migrating birds flew nonstop for 200 days.
That's right, the birds remained airborne for more than six months, eating, drinking and sleeping on the fly, so to speak. Swiss scientists recently published their findings in the journal Nature Communications.
Since the 1970s, ornithologists have speculated that the Alpine swift's smaller cousin, the common swift, stayed airborne for much of the year, although that concept is based mostly on short-term radar data.
In fact, only aquatic animals like dolphins have been proven capable of such long-term locomotion. (Unlike humans, dolphins sleep by resting one half of their brain at a time.)
Recently however, researchers at the Swiss Ornithological Institute and the Bern University of Applied Sciences, captured six Alpine swifts prior to their epic migration to Western Africa.
Each of the birds was harnessed with an electronic monitor that was slightly smaller than a postage stamp.
The devices used sunlight to track the bird's location, and also measured changes in their body position and movement.
When the birds returned to Switzerland six to seven months later, three of them were recaptured and their data downloaded. (Monitors with radio transmitters would have been too heavy for the birds.)
At first, lead study author and ornithologist Felix Liechti said he did a double-take when he looked at the data. From late September until about early spring, it appeared the birds did not stop moving.
"It seemed to me unlikely that they did not rest somewhere on trees or cliffs," Liechti said. "I was very surprised."
What Liechti and colleagues found was that during the daytime, the birds activity and pitch measurements showed that they were not resting on the ground. Also, at night the birds greatly reduced their wing flapping and appeared to be gliding for long distances. 
And how did they eat and drink?
Swifts feed on so-called aerial plankton, bugs and spiders that are swept into the sky by high winds. Scientists believe they get much of their water from this prey, however they are able to skim ponds and lakes while in flight, like swallows, Liechti said.
The epic flight began just after mating season in Europe and seemed to last throughout their wintering time in Africa. Only when the birds began to return to Europe in the spring, and had crossed the Sahara Desert, did they appear to take rest breaks.
"I think this might have had to do with limited food resources in the air," Liechti said.
It remains unclear why the birds would choose to expend so much energy on long-haul flights.
"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."