David M. Larson
Every year in Mass Audubon's Birder's Certificate Program, when I am presenting information about avian physiology, I mention the amazing phenomenon of the migration of Bar-headed Geese. These birds migrate between their wintering and nesting grounds over the Himalayan Mountains and Tibetan Plateau, at 5000–6000 meters (approximately 16,000–20,000 feet), and have been seen in flight at almost 7300 meters (24,000 feet). In comparison, human mountain climbers commonly use bottled oxygen above 7000 meters. Combining the metabolic demands of flapping flight (already metabolically expensive), the greater exertion required to fly in the lower air pressure at altitude (thinner air requires faster flight to maintain lift), and the decreased oxygen concentration at altitude, makes flying to this level pretty impressive.
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