Birds rarely exceed an altitude of 500 feet. The high wind speeds at altitude make it hazardous, plus it takes a lot of energy to achieve such heights. Some birds have no choice though, as their migration paths take them over mountains. Long distance migrant birds cruise at altitudes of more than 10,000 feet, where there is less air resistance. The energy savings during a long migration compensate for the energy used to achieve such heights.
Clearing the Himalayas
Bar headed geese are noted as some the highest flying of all birds, capable of peaking at 21,120 feet. Their migration path takes them over the Himalayas, where they have to clear some of the highest peaks on Earth. The bar headed geese spends most of its time in India, but it migrates to Mongolia in spring and the only way to get there is by traversing the Himalayas. The entire migration covers approximately 5,000 miles and can take two months, but the geese can clear the mountain range in just eight hours. What makes this high altitude flying more impressive is that the bar headed goose doesn’t receive the benefit of updraft. They start from sea level and use their own strength to climb.
A flock of whooper swans were recorded by radar flying at 29,000 feet coming into land in Northern Ireland. This makes them the highest flying birds on record. To achieve such heady heights, birds rely on their lungs to perform efficient oxygen extraction. Without air pressurization, these altitudes would kill humans and other mammals, but birds’ lungs are much better adapted to deal with the lower oxygen levels of such altitudes.
A High Starting Point
The rare Sillem’s mountain finch has no choice but to fly at high altitudes, for his home is the Tibetan plateau, which rises to 16,500 feet. That’s three times higher than the city of Denver. So from this elevated starting point, Sillem’s mountain finch already is higher than the maximum altitude of most birds. Scientists believe that this high altitude home has kept this extremely rare species free from human interaction and that it benefits from that lack of interference.
Scanning the Land Below
Vultures are high flyers too, but they are a rarity in that migration isn’t their motivation. While most birds wouldn’t waste the energy in climbing above 500 feet, there is a direct payoff from doing so for vultures. Once at an altitude of around 10,000 feet, they use their excellent eyesight to scan the landscape below from a relatively static aerial position. Instead of flying over a larger distance, they use elevation to expand their field of vision. If they spot a meal down below, the climb has an immediate payoff.
Other High Flyers
Buzzards, falcons, harriers, swallows, kites, swifts and herons all perform long distance migrations and use the thinner air at high altitudes to make the flight easier. The typical optimum cruising altitude for these birds is around 1,135 feet. Scientists monitoring the migratory behavior of these birds observed that once they hit an altitude with a decent tailwind, they stopped ascending, even if better tailwinds were available at higher altitudes.
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