A high-flying duck species reaches an altitude of upto 6,800 metres (22,000 feet) to cross the Himalayas, finds a recent study.
Ruddy shelducks are known to breed north of the Himalayan mountain range, but spend their winters at the 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 terrains higher than 4,000 metres, where oxygen levels are halved.
Scientists from the University of Exeter used satellite tracking to discover that they fly through valleys in the mountain range - avoiding massive peaks like the Mount Everest.
"This is the first evidence of extreme high-altitude flight in a duck," said lead researcher Nicole Parr.
"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," Parr added.
They also showed that the ruddy shelduck has a faster climb rate than the bar-headed goose - the only waterfowl known to fly even higher.
They also suggested that the bar-headed geese may not be the only species flying at these high altitudes.
However, more research is needed to find out whether ruddy shelducks reach similar heights to the bar-headed 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 metres and sometimes go as high as 6,800 metres.
They suggested that ruddy shel ducks wintering further east in India may fly even higher, given the higher terrain that lies north of India.
The research appeared in the Journal of Avian Biology.