Tuesday, July 16

Power naps and eating on the wing en route from Britain to southern Africa



The common swift stays constantly airborne for up to ten months at a time, new research reveals.

The bird, ubiquitous in the UK and Europe, conserves energy by riding currents of hot air and taking power naps as it slowly glides from high altitudes.

Scientists tracked 19 of the creatures as they completed two of their annual migratory cycles to Central Africa via West Africa and found three did not once touch the ground.

It’s mind-boggling that they can stair airborne for 10 months without needing to come downProfessor Anders Hendenstrom

The others spent all but half a percent of their cumulative flight time in the air, only landing due to emergencies such as violent weather.

While there have been other examples of birds remaining in flight for periods of months, the evidence on common swifts sets a new record, the researchers say.

Up till now the species capable of the longest continued flight was believed to be the Alpine Swift, with a six-month flight recorded, while a frigate bird has been recorded non-stop in the air for two months.

Lead researcher Anders Hendenstrom, professor of biology at Lund University, said: “It’s mind-boggling that they can stair airborne for 10 months without needing to come down.

“Most of the time there is a trade-off between energy use and life: live hard and die young.

“But these birds live quite long, up to 20 years, so somehow they have beaten this rule.”

Common swifts live off airborne insects and fly south from their European breeding grounds as food supplies dwindle when the weather gets cold.

The scientists attached sensors to the animals and found that their flight activity appeared higher at night, most probably because the birds spent their days soaring on warm air currents.

They also discovered that at least twice a day – usually dawn and dusk – the common swifts would climb to around 10,000 ft.

The altitude afforded the birds roughly half an hour’s slow descent when they would have been able to sleep, said Prof Hadenstrom.

“It would give them plenty of time for a power nap,” he said.“We don’t know for sure that they went to sleep but it’s logical to assume so because all animals need sleep.

“The fact that some individuals never landed during 10 months suggest they sleep on the wing.”

The long life of the common swift means that the accumulated flight distance of a single bird equals seven round-trip journeys to the moon,” he added.

The species typically leave their northern breeding grounds in July or August, returning in May.

Scientists had long ago proposed that swifts might be spending most of their lives in flight, but until now the theory had not been proved.

Published in the journal Current Biology, the study describes how the researchers used a new type of micro data logger and light sensors to record the birds’ precise location and altitude.

Nineteen were subsequently recaptured after their flights between 2013 and 2015.

Researchers believe the common swift’s extreme energy efficiency is down to aerodynamic wings and thin body.

The bird appears roughly similar in size to the barn swallow or house martin, with a 16-inch wingspan despite being only about 6.5 inches long.

Prof Hadenstrom said the next research task was to prove exactly when and for how long the species managed to sleep during flight.