WASHINGTON, Oct. 29 (Xinhua) -- Scientists had long ago proposed that common swifts, a medium-sized migratory bird, might spend most of their lives in flight, but it is only now that they have managed to prove that these birds can actually fly for most of the year -- 10 months -- without landing.
"This discovery significantly pushes the boundaries for what we know about animal physiology," lead author Anders Hedenstrom of Lund University in Sweden, said in a statement.
"A 10-month flight phase is the longest we know of any bird species -- it's a record."
Previously, scientists have found frigate birds and alpine swifts can remain in flight for up to seven months.
The new findings were published this week in the U.S. journal Current Biology.
For this study, the researchers followed 13 individual birds, some of them for two years in a row, using a microdata log that was attached to each bird in southern Sweden.
These data loggers enabled the researchers to determine whether the birds were in the air or not, their acceleration, and where they had been at any given time after leaving their breeding site in August for a migration to Africa and before returning for the next breeding season 10 months later.
The results showed that some of the birds landed during short periods at night, sometimes during an entire night. But even these birds spent more than 99.5 percent of their 10-month migration and hibernation period in the air.
Data from other birds showed that they did not land a single time in ten months.
The birds' flight activity often appeared lower during the day than at night, most likely because the birds spent their days soaring on warm air currents, the researchers said.
Hedenstrom said the researchers don't yet know whether or how the birds sleep but "the fact that some individuals never landed during 10 months suggests they sleep on the wing."
Perhaps they find time to nap during slow descents at dawn and dusk, he suggested.
Despite the high energetic costs associated with all that flight, common swifts also manage to live surprisingly long lives, contrary to popular notions about living hard and dying young.