The roller coaster flight strategy of bar-headed geese conserves energy during Himalayan migrations

How the bar-headed geese, a 3 kg bird affront their migration across the Himalayan range?

The big question that was motivation of several documentaries was finally answered in a paper recently published in Science.

Twice a year, around 100.000 bar-headed geese migrate from Mongolia to the Indian coast. A trip of approximately 4.500 km that crosses the Himalayan range. Researchers discovered that the geese prefer to fly during the night as low as possible and without needing help from the wind. The animals do not stop beating their wings and can reach as high as 5.000 meters over sea level (flying over the 5th highest peak in the world) and descend 1.000 meters in few minutes to ascend again. The scientists compared their trip to a aerial roller coaster ride.

On average, the geese flew at an altitude of about 4500 meters, but often they changed altitude. For example, one of the four birds whose data was retrieved dropped 1000 meters in 20 minutes, then climbed more than 2000 meters in the next 1.5 hours. Yet, one bird  has been tracked migrating as high as 7290 meters, an altitude where many humans would require supplemental oxygen to move.

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