Common swifts (Apus apus) may not be the biggest of birds, but they're proving to be some of the most powerful flying machines in the world.

Researchers in Sweden have confirmed a popular theory that swifts can stay in flight for long periods of time. In fact, these medium-sized birds can remain airborne for 10 straight months without having to land.

In a study featured in the journal Current Biology, Lund University researcher Susanne Åkesson and her colleagues attached data loggers to 19 common swifts in 2013 and 2014 in order to record their flight data. They then recaptured the animals after a few months.

The devices that the researchers placed on the birds measured the animals' acceleration and activity during flight. The ones that were attached to the swifts also featured trackers that monitored the birds' geolocation.

Åkesson and her team discovered that the birds can spend almost their entire 10-month nonbreeding period every year without needing to land.

One swift that the researchers observed only stopped flying for four nights in 2014. The following year, this exact same bird only took a break from its flight for two hours.

While most of the other swifts took breaks for longer periods, the time they spent resting is still considerable small compared to when they are in flight, the researchers said.

No Sleep, No Worries

According to the National Geographic, common swifts are known to fly from Europe down to the sub-Saharan part of Africa. However, the birds don't seem to land in the area, as evident in the lack of roosting sites found in sub-Saharan Africa.

Åkesson and her colleagues believe that swifts take a break from flying during their nonbreeding season only to avoid bad weather. This seemingly nonstop flight suggests that these birds may not necessarily need to pause to sleep. The researchers said nobody knows exactly when swifts choose to sleep and for how long.

"They feed in the air, they mate in the air, they get nest material in the air," Åkesson said. "They can land on nest boxes, branches, or houses, but they can't really land on the ground."

This apparent inability to land may be explained by the swifts' body shape. The National Geographic says the birds are known to have very long wings but short legs, which makes it difficult for them to take flight from flat surfaces.

As for the swifts' propensity for long sustained flight, the researchers believe it may have something to do with their preferred food. The birds mainly feast on insects found in high-altitudes, making it necessary for them to master efficient flight.

However, this also means that swifts had to trade off their ability for territorial locomotion. Staying on the ground for long periods would make them more vulnerable to parasites and predators.

Photo: Stefan Berndtsson | Flickr