Bar-Headed Geese Fly in Roller Coaster Pattern at High Altitudes (VIDEO)

Bar-headed geese have some stunning migratory behavior. They fly at extremely high altitudes across the Tibetan plateau and the Himalayan Mountains. Now, scientists have taken a closer look at these birds and have found how the geese cope with flying in the relatively low-density mountain atmosphere.

In order to get a better look at these birds, the researchers used custom-designed data loggers to monitor pressure-derived altitude, body accelerations and heart rate of geese during their southern migration from their breeding grounds in Mongolia to their wintering grounds in south-eastern Tibet or India.

In the past, researchers assumed that bar-headed geese would fly to high altitudes relatively easily and then remain there during their flights, possibly benefitting from a tailwind. This latest study, though, reveals that the geese perform a kind of roller coaster ride through the mountains, essentially tracking the underlying terrain even if this means shedding hard-won altitude.

So why do they do this? Flying at progressively higher altitudes becomes more difficult, since the decreasing air density reduces the bird's ability to produce the lift and thrust required to maintain flight. The birds also face reduced oxygen availability. What helps is that the geese rely on updrafts, which is wind that is deflected upwards by the ground. This provides additional rates of ascent and a reduction in energy costs.

"The physiology of bar-headed geese has evolved in a number of ways to extract oxygen from the thin air at high altitudes," said Graham Scott, one of the researchers, in a news release. "As a result, they are able to accomplish something that is impossible for most other birds."

The findings are published in the journal Science.

Want to learn more? Check out the video below, courtesy of YouTube.

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