A small, dark-feathered bird known as the common swift flies for 10 months on end without ever landing, the longest time spent aloft of any known bird, scientists said.
The findings in the US journal Current Biology confirmed a 46-year-old hypothesis, first offered by British researcher Ron Lockley, that these birds spend most of their lives in the air.
A team of researchers from Sweden fitted tiny backpacks on 13 of the brownish-black birds.
Weighing only one gram, these microdata logs recorded whether the birds were in the air or not, their acceleration and where they had been at any given time.
"When the common swifts leave their breeding site in August for a migration to the Central African rainforests via West Africa, they never touch ground until they return for the next breeding season 10 months later," said researcher Anders Hedenstrom of Lund University in Sweden.
"Some individuals may roost for brief periods, or even entire nights in mid-winter, but others literally never landed during this period."
Those who did stop did so only briefly, and spent 99.5 percent of the 10 months in the air.
The birds catch food while in flight, according to the study.
Researchers said they still don't know if or how the birds sleep during this time, but suggested that they might catch a few winks when they fly to high altitudes each day at dawn and dusk, and then slowly descend.
During the day, they probably save energy by gliding in upward currents of warm air.
"This discovery significantly pushes the boundaries for what we know about animal physiology," said Hedenstrom.
"A 10-month flight phase is the longest we know of any bird species -- it's a record."
Other kinds of birds, such as the frigate bird, are known to sleep while gliding.