The route, in numbers
Bar-headed geese (Anser indicus) breed on the high-altitude lakes of Central Asia, Tibetan plateau, Mongolia, China, and winter on the Indian subcontinent, including the wetlands of Assam, Rajasthan, and the Gangetic plains. Twice a year, they cross the Himalayas. The recorded ceiling for this flight is 7,290 metres above sea level. At that altitude, atmospheric oxygen pressure is roughly one-third of what it is at sea level. A human being at that height, without supplemental oxygen, loses consciousness within minutes. The geese fly through it, often at night, sometimes in a single continuous push of 8 hours or more.
