High(est) flying birds
Some birds fly higher than others. Here's a collection of the undaunted heroes of air travel - a few of these birds even almost reach the air lanes of planes.
Rüppell's vulture: 11,300 metres (37,100 feet)
Vultures usually don't travel long distances, instead, they rise to expand their field of vision. Their excellent eyesight allows the critically endangered species to scan the landscape below from a relatively static aerial position.
Common crane: 10,000 metres (33,000 feet)
The Common crane is a long distance migrant. Important staging areas exist anywhere from Sweden and Germany to China. The height stated here was recorded above the Himalayas.
Bar-headed goose: 8,800 metres (29,000 feet)
The birds also fly over the peaks of the Himalayas on their migratory path. Studies have found that they breathe more deeply and efficiently under low oxygen conditions.
Whooper swan: 8,200 metres (27,000 feet)
The Whooper swan is the Eurasian counterpart of the North American trumpeter swan. It's also the national bird of Finland, featured on the country's 1 euro coin.
Alpine chough: 8,000 metres (26,500 feet)
These birds are able to breed in high mountain areas because their eggs have less pores than those of lowland species and don't try out as quickly. The bird's embryos also seem to be genetically predisposed to absorbing particularly large amounts of oxygen.
Bearded vulture: 7,300 metres (24,000 feet)
Bearded vultures are listed as 'near threatened' by the IUCN. And you had better not hunt them, because according to Iranian mythology the birds are a symbol of luck and happiness. Whoever shoots one is supposed to die within forty days.
Ruddy shelducks: 6,800 metres (22,000 feet)
It was just discovered that these duck-like waterfowls are among the world's highest flying birds. Like many others on this list, they cross the Himalayas to get to their breeding grounds.