The geese have been recorded at heights of more than 7,000m (23,000ft).
Now, a team led by researchers from Bangor University has tracked the flight and revealed the basis for the birds’ “rollercoaster flight” pattern.
The findings, published in Science, show how the birds hug the mountainous terrain, and that this saves energy.
Bar-headed geese have fascinated biologists for decades.
They achieve physiological feats that seem impossible – flying at extreme altitude, where there is less than 10% the oxygen found at sea level.
George Lowe, the New Zealand born climber who supported Edmund Hillary and Tenzing Norgay’s ascent in 1953, said he had seen the geese flying over the top of Mount Everest – the peak is approximately 29,000ft.
And, using GPS trackers, this team has recorded one bird flying at 24,000ft.
The implanted devices also measured the acceleration, body temperature and heart rate of seven geese, caught in central Mongolia.
Data from these devices enabled the scientists to work out the birds’ energy use, as well as tracking what they called their “rollercoaster” flight pattern.
While rising and falling may seem wasteful – losing hard-earned altitude, just to climb again later – these unique trackers revealed the reasons behind it.