Check out this thread:
http://www.pprune.org/forums/showthread.php?t=197260
It includes a link to a story on bar-headed geese, a specially adapted bird that flies
over Mt. Everest every year.
http://magazine.audubon.org/birds/birds0011.html
At 29,028 feet, Mount Everest is tall enough to poke into the jet stream, a high-altitude river of wind that blows at speeds of more than 200 miles an hour. Temperatures on the mountain can plummet low enough to freeze exposed flesh instantly. Its upper reaches offer only a third of the oxygen available at sea level--so little that if you could be transported instantly from sea level to Everest's summit, without time to acclimatize, you would probably lose consciousness within minutes. Kerosene cannot burn here; helicopters cannot fly here. Yet every spring, flocks of bar-headed geese--the world's highest-altitude migrants--fly from their winter feeding grounds in the lowlands of India through the Himalayan range, sometimes even directly above Everest, on their way to their nesting grounds in Tibet. Then every fall these birds retrace their route to India. With a little help from tailwinds, they may be able to cover the one-way trip--more than 1,000 miles--in a single day.