Bar-headed Geese, champions of high-altitude migration, leave their nesting grounds in Tibet and scale the Himalayan range on their way to wintering grounds in the lowlands of India. How do they do it? These geese have a breathing structure that extracts oxygen from thin air, even at 30,000 feet. Inhaled air passes through the lungs and is temporarily stored in several sacs, then circulated back through the lungs. The capillaries in their breast muscles are more numerous than in other birds, providing the muscles with a greater supply of oxygen.

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