The alpine swift has some incredible stamina.

The bird with a wingspan of 22 inches can fly uninterrupted for 200 days, a new study suggests. The findings, published in the journal Nature Communications, show how six of the birds stayed airborne for more than six months without landing.

"It seemed to me unlikely that they did not rest somewhere on trees or cliffs," lead study author and ornithologist Felix Liechti told the Los Angeles Times. "I was very surprised."

Researchers followed half a dozen of the alpine swift during their migration from Switzerland to West Africa. The birds were tracked with data loggers. While only three were recaptured at the end of the migration period, they provided enough information to show that the swifts remained in the air for 200 days straight.

“Their activity pattern reveals that they can stay airborne continuously throughout their nonbreeding period in Africa and must be able to recover while airborne," the team wrote in the study. "To date, such long-lasting locomotive activities had been reported only for animals living in the sea."

The instruments attached to the birds monitored the intensity of daylight and used accelerometers to measure the birds’ activity in a 3.2 second window every 4 minutes. Throughout their nearly 1,300 mile migration the birds never rested. Their large wingspan allowed them to glide instead of resting on perches -- which may be when the birds catch some shuteye, ScienceNow reports.

“We didn’t expect them [to] keep flying all day and all night long during their stay in Africa,” Liechti said, adding that the birds may function like dolphins that use only half of their brains to sleep at a time.

Much like migrating sea animals, alpine swift rely on aerial plankton for food. Tiny bacteria including fungus, seeds, spores and insects swept in the air allow the swifts to eat without taking a break, according to LiveScience. This diet may be the reason why the alpine swift remain airborne for so long. Liechti says their continuous flight may help the birds exploit food sources that other birds don’t have access to, avoid predators and parasites.

“These aren’t very convincing,” Liechti told National Geographic referring to the possible theories surrounding the alpine swift, “but for sure, there’s a cost to staying in the air, so there must be a benefit.”