STEVE INSKEEP, HOST:
In the world of animals that travel, the bar-headed goose stands out.
(SOUNDBITE OF BAR-HEADED GOOSE CALL)
INSKEEP: And also sounds off. Every year, this huge, white-and-black bird travels from Central to South Asia, which means flying over the Himalayan Mountains. NPR's Nell Greenfieldboyce reports that researchers recently did an unusual study to see how the birds tackle this high-altitude challenge.
NELL GREENFIELDBOYCE, BYLINE: There's one report of these geese flying over Mount Everest. That's unconfirmed, but these birds do fly high.
CHARLES BISHOP: You know, they're traveling through some of the most difficult terrain on Earth in temperatures of minus 20 or minus 30 through 500 kilometers of steep, beautiful, but ice- and snow-covered mountains.
GREENFIELDBOYCE: Charles Bishop studies bird flight at Bangor University in the United Kingdom. He wanted to know how the geese do it.
BISHOP: My interest is kind of understanding how animals actually work; how much energy does it take to fly; how high do they go; how difficult are their journeys?
GREENFIELDBOYCE: To find out, a team headed to Mongolia. They captured geese on a lake and did a little bit of avian surgery. They implanted tubes filled with sensors to record the birds' altitude, how quickly they beat their wings and their heart rates. The next year, after the migration, the researchers managed to recapture some of the birds and get the data. Bishop says they had thought the geese might climb to a high altitude and then stay up there, like an airplane.
BISHOP: We know that they've been spotted occasionally at very high altitudes over 7,000 meters by climbers.
GREENFIELDBOYCE: To their surprise, the geese actually flew up and down, up and down, like a roller coaster.
BISHOP: They climb, get over an obstacle, and they go back down again. And they just seem to be tracking the terrain.
GREENFIELDBOYCE: Bishop and his colleagues figured out that flying high up in thin air is really hard. The geese have to flap their wings a little faster. This makes their heart rates go way up. So they drop back down as soon as they can. Doug Altshuler is a flight researcher at the University of British Columbia.
DOUG ALTSHULER: What's so amazing about this is that they're actually able, by doing this, to transverse, you know, one of the hardest migration passages of any bird and yet do so within a physiological zone that's comfortable for them.
GREENFIELDBOYCE: The new findings appear in the journal Science. Nell Greenfieldboyce, NPR News.