Who needs land? These birds spend 10 months of the year in flight
Make no mistake, the tiny common swift found throughout Europe and much of Asia is a lean, mean flying machine.
A new study reveals that these birds spend nearly their entire lives in flight — even eating, mating, molting and probably sleeping on the wing.
Researchers at Lund University in Sweden equipped adult swifts with data loggers to track the birds’ movements as they embarked on their epic 10-month migration from Europe to sub-Saharan Africa and back. (The other two months of the year are spent hatching and raising chicks.)
When the scientists recaptured 19 of the birds as they returned to their nests one or two years later, the loggers showed that the birds almost never stopped to rest during their intercontinental journeys. In fact, three birds literally never stopped flying for the entire 10 months.
The birds that did land took only short breaks, which never amounted to more than 0.5% of their travel time, said biologist Anders Hedenström, who led the study published Thursday in Current Biology. That means common swifts spend more than 99% of the migratory period airborne.
“There is no need for them to [land] unless they are forced to [because] they encounter very bad weather,” Hedenström said.
The study resolves a longstanding conundrum that has puzzled ornithologists for decades. Every August, the common swift leaves its breeding site in the northern reaches of Europe and makes the long journey to the rainforests of central Africa. They return the following June.
At home, large flocks of the birds are commonly seen roosting in trees or on buildings, but along their nearly 6,000-mile flight plan, no one has ever found a sign of even a temporary resting place. Perhaps, scientists thought, the swifts never touch the ground during their migration.
Using accelerometers to record when the birds were flapping their wings or holding still (most likely on the ground) and light sensors to track their location, Hedenström and colleagues proved this to be true. That means the common swift holds the record for the longest continuous flight time of any bird.
Alpine swifts can fly up to six months without stopping, and great frigate birds, with their giant 7½-foot wingspans, can soar across the Indian Ocean for about two months on end. But the common swift appears to have gone all-in on its aerial lifestyle.
Weighing just 1.5 ounces, these little birds sport a relatively wide 16-inch wingspan. Their long, narrow wings and streamlined body shape generate minimum drag. In other words, they’re built for efficient flight.
Swifts eat on the go, nibbling on moths or other insects and spiders swept into the air by the wind. They molt feather by feather, so they’re never rendered flightless like other birds.
During the day, they save energy by gliding on rising currents of warm air. It’s possible, Hedenström said, that they also sleep while gliding — though more research is needed to see how they manage to sleep in flight.
The birds only really land to lay their eggs. The swifts nest in tree holes bored by woodpeckers, rock cavities or in the eaves of houses and buildings.
As the species adapted to feeding on prey in the air, they compromised more of their land-based abilities.
“They are very clumsy on the ground, for example, [and] they would easily fall victim to predators,” Hedenström said. “They really look awkward when they crawl around in their nest.”
Despite their long-hauling lifestyle, some of the oldest swifts still live up to 20 years, Hedenström said. In that time, the bird could have flown the equivalent distance to the moon and back seven times.
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