The highest flying bird is the bar-headed goose, which can reach heights of around 21,120 feet. However, these geese typically travel at lower heights for most of their flight.
The bar-headed geese often follow valleys when flying through the mountains, and generally remain at an altitude of 18,000 feet. However, they do sometimes fly into higher altitudes for a short duration of time. The geese often fly to Mongolia and nearby areas to breed for their annual spring migration. During this flight, they need to fly over the Himalayan mountain range, the tallest mountain range in the world. The Himalayan range also contains the world's highest mountain, Mount Everest, which reaches a height of 29,035 feet. The bar-headed geese must fly over this range, including directly above Mount Everest, to reach their breeding grounds.
In order to reach such extreme heights during their migration, the bar-headed geese are biochemically and physiologically adapted to their surroundings. The birds are then able to fly at altitudes with very low oxygen levels and temperatures. This goose weighs close to five pounds and stands nearly two feet tall. It has a long neck along with a short, tapered beak, helping to create a stunning S-shaped silhouette.