A high-flying duck species reaches altitudes of up to 6,800 meters (22,300 feet) to cross the Himalayas, new research shows.

Ruddy Shelducks breed north of the Himalayan mountain range and spend their winters at sea level south of the Tibetan Plateau. They need to fly over the Himalayas in the spring to get back to their breeding grounds, a huge challenge that sees them cross terrain higher than 4,000 meters, where oxygen levels are halved.

Scientists from the University of Exeter used satellite tracking to discover that the ducks fly through valleys in the mountain range — avoiding massive peaks like Mount Everest. They reported the findings in a paper in the Journal of Avian Biology.

“This is the first evidence of extreme high-altitude flight in a duck,” says lead researcher Nicole Parr of the Centre for Ecology and Conservation at the University of Exeter. “This species has probably evolved a range of adaptations to be able to cope with flying so high, where oxygen levels are half those at sea level. We don’t yet know the nature of these adaptations.

“Our research also shows that the Ruddy Shelduck has a faster climb rate than the Bar-headed Goose — the only waterfowl known to fly even higher.”

In 2014, Bar-headed Geese were tracked flying near Everest at 7,290 meters (23,900 feet). They were long thought to be the world’s highest-flying bird based on flapping flight (some birds soar higher on thermals), but the new research suggests that the geese may not be the only species flying at these high altitudes.

More research is needed to find out whether the shelducks reach heights similar to the geese.

The scientists used satellite data collected from 15 Ruddy Shelducks from two populations spending their winter south of the Tibetan Plateau. They found the birds, which take a circuitous route to avoid mountain peaks, regularly fly above 5,000 meters and sometimes go as high as 6,800 meters.

The researchers suggested that shelducks wintering farther east in India may fly even higher, given the higher terrain that lies north of India.

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Originally Published September 6, 2017