Birds migrating over large distances often select higher altitudes to take advantage of favorable winds. Some birds have been observed at very high altitudes. Geese can fly over the highest mountain, Mount Everest, at an altitude above 29,000 feet. In South America, the Condor has been observed at altitudes close to 20,000 feet. A vulture collided with a jetliner over West Africa at an altitude at an altitude of 37,000 feet.
Birds are the most mobile creatures on Earth.
Many species migrate from the northern hemisphere to the southern hemisphere each year. Some seabirds spend long periods of time, possibly years, in the air without landing, and may travel from one side of the planet to another. The champion migrant, however, is the Arctic Tern. These birds move each year from their nesting grounds in the far northern regions of the north to the coasts of Antarctica in the southern hemisphere, a round trip of 22,000 miles. Someone has actually counted the number of feathers on many species of birds.