Ornithology
The bar-headed goose (Anser indicus) is a medium-sized goose renowned for breeding in Central Asia and wintering in South Asia, making one of the highest-altitude migrations of any bird. It is famous for crossing the Himalayas at altitudes exceeding 7,000 meters, where oxygen levels are less than half those at sea level. Its remarkable physiology has made it a model species for studying high-altitude adaptation.
The bar-headed goose was first formally described by John Edward Gray in 1832 under the name Anser indicus, and it is placed in the genus Anser alongside other grey geese. It is distinguished by two bold black bars on the back of its white head, which give the species its common name. The body is pale grey with a white neck and a black-edged white rear, and the bill and legs are orange-yellow. Adults measure 71–85 cm in length and weigh 1.9–2.9 kg, with males typically larger than females. Juveniles lack the head bars and have a duller plumage, making them confusable with other grey geese until their first winter.
The bar-headed goose breeds on high-altitude lakes in Mongolia, western China, and Tibet, and winters in India, Pakistan, and Nepal. During migration, it crosses the Himalayan range, with satellite tracking confirming flights at altitudes above 7,000 m, and one record of a bird flying at 7,290 m over Mount Everest. These flights are remarkable because the air density and oxygen partial pressure are extremely low, yet the geese sustain flapping flight for hours. Unlike many birds that migrate at night, bar-headed geese often fly during the day, taking advantage of updrafts and mountain winds to reduce energy expenditure. They also exhibit a 'roller-coaster' flight pattern, closely following the terrain rather than maintaining a constant altitude, which minimizes the time spent at the highest elevations.
The bar-headed goose possesses a suite of physiological adaptations that enable its extreme high-altitude flights. Its hemoglobin has a higher oxygen-binding affinity than that of other geese, due to specific amino acid substitutions that increase the molecule's affinity for oxygen. The bird also has a larger heart and more capillaries in its flight muscles, facilitating oxygen delivery. During flight, it hyperventilates to a greater extent than sea-level birds, and its hemoglobin's affinity is less sensitive to pH changes, allowing continued oxygen uptake despite respiratory alkalosis. Additionally, the mitochondria in its muscle cells are more efficient at using oxygen, and it can tolerate lower blood oxygen levels without losing consciousness.
Beyond its famous migration, the bar-headed goose has several lesser-known traits. It is one of the few geese that perches in trees, a behavior more common in ducks, and it often nests on cliffs or in tree hollows, unlike ground-nesting geese. The species is also known for its aggressive defense of nesting territories, with both parents attacking intruders, including large mammals. In captivity, bar-headed geese have lived over 30 years, and they are popular in waterfowl collections. A notable historical record: in 1953, a bar-headed goose was found dead on the summit of Mount Everest by the Swiss expedition, providing early evidence of high-altitude flight. The species is also a carrier of avian influenza viruses, and its migration routes have been studied to understand disease spread.
This article is based on peer-reviewed research and authoritative ornithological sources.
Help improve the encyclopedia. Reports go straight to the site manager.