If you've ever been hiking at high altitudes you probably know how thin the air gets. This makes a lot of people sick. But how do birds do it, like say, the bar-headed goose, which flies up 30,000 feet when they soar over the Himalayans?

Scientists now think they know, according to a short item in the New York Times. There's only about a quarter of the oxygen available that high compared with sea level. Yet, they flap and fly.

Turns out the birds' muscle have adapted, according to an article in The Proceedings of the Royal Society B: Biological Sciences by a doctoral student at the University of British Columbia.

The muscle fibers are the same as other less high-flying geese. But the bar-headed geese have more capillaries around and within individual muscle cells and oxygen doesn't have as far to travel to mitochondria, or cell membrane, which uses the oxygen to supply energy to the cell.

Just thought that was kind of interesting.

Getty Images photo of a bar-headed goose