An international team of scientists that includes Dr. Graham Scott in the Department of Biology have revealed how bar-headed geese (Anser indicus) fly at high altitudes during their migration across the Himalayan mountains, in an article published in the January 16 issue of Science. The study used custom-designed data loggers to measure heart rate, body acceleration, and temperature during the southward migration from their breeding grounds in Mongolia to their wintering grounds in India. The new study shows that the geese perform a sort of roller coaster ride through the mountains that helps them save energy and complete their challenging migration.
Historically, it was commonly assumed that bar-headed geese would fly to high altitudes relatively easily and then remain there during their flights, possibly benefitting from a tailwind. However, the study found that flying becomes progressively more difficult for the geese at higher altitudes, where there is less oxygen in the air to breathe and the reduced air density decreases the bird’s ability to produce the lift and thrust required to maintain flight. By tracking the underlying terrain, even if this means repeatedly shedding hard-won altitude only to have to regain height later in the same or subsequent flight, the birds were able to reduce the energetic costs of their migration. On occasion, they also flew in relatively strong updrafts of air to reduce the work needed to stay aloft. The geese are thus able to fly across the world’s highest mountains while remaining comfortably within their physiological capabilities. How is this possible? “The physiology of bar-headed geese has evolved in a number of ways to extract oxygen from the thin air at high altitudes”, said Dr. Graham Scott. “As a result, they are able to accomplish something that is impossible for most other birds.”
The article can be found on the Science website, at http://www.sciencemag.org