Winging it (Image: Varesvuo/NaturePL)

Swifts are said to spend most of their lives airborne, but no one has ever proved this. Now, a study suggests there’s some truth to it: alpine swifts spend more than six consecutive months aloft, not even resting after migrating to north Africa following their breeding season in Europe.

“Up to now, such long-lasting locomotive activity had been reported only for animals living in the sea,” says Felix Liechti of the Swiss Ornithological Institute in Sempach.

Liechti and his colleagues attached 1.5-gram data loggers to three alpine swifts (Tachymarptis melba) at a Swiss breeding site, and recaptured the birds the following year. The loggers recorded the birds’ acceleration and geographic location. The measurements suggest that for 200 days, all three swifts remained airborne while migrating to and wintering in Africa.


Liechti says researchers have previously asserted but never proved that newborn common swifts spend three years aloft before landing for breeding.

Truly amazing

“Amazing, truly amazing,” says Carsten Egevang of the Greenland Institute of Natural Resources in Nuuk of Liechti’s findings. “We knew that swifts stay on the wing for long periods, but 200 days is very impressive.”

The birds survive on airborne plankton, and almost certainly sleep on the wing too, Liechti says. “It has been assumed that the birds ‘sleep’ only for seconds, or use only one half of the brain while the other half is resting,” he says.

But some researchers think the swifts might not sleep at all. “Our group has shown that dolphins and killer whales remain active for at least 90 days without sleep and with greatly reduced sleep for up to 150 days after birth,” says Jerry Siegel of the University of California at Los Angeles. He also cites recent work showing that sandpipers stay awake for weeks during breeding, and that dolphins can function without impaired performance for as long as 15 days without sleep.

“What all this work tells us is that when it is adaptive for animals to remain awake, evolution allows that, so I think the idea that swifts must sleep and are therefore ‘sleep-flying’ is incorrect,” says Siegel.

Journal reference: Nature Communications, DOI: 10.1038/ncomms3554