Bar-headed geese are known for their exhausting migration route over the Himalayas, reaching extreme heights up to 10,175m and traveling distances of 1500km in a single day. Although it was already known these high-flyers are physiologically and biochemically adapted to flying at these altitudes where oxygen levels and temperatures are both extremely low, it remained unclear how they performed this incredible energy-costly feat.
Previously, researchers hypothesized the geese must use the prevailing winds to ease their flight across the world’s highest mountains. Now a new paper published in Proceedings of the National Academy of Sciences (online) reveals the geese actually fly mostly throughout the night when winds are light and actually cross the Himalayas in a single 8 hour flight!
The authors suggest early flight could be more energy efficient because the cooler morning air is denser than warm air, giving them more uplift with each wingbeat as well as reducing the amount of heat dissipation for their activity. Further, since stormy weather is more common in the Himalayas during the afternoon the geese might strategically avoid flying at these times higher to maximize safety and control during flight.