Bar Headed Goose Climb
The Bar-headed Goose is a goose which breeds in Central Asia in colonies of thousands near mountain lakes. Drs. Charles Bishop and Lucy Hawkes, from Bangor University, and a large international team of researchers, report that bar-headed geese can fly climb up to 6,000 meters in only 8 hours while passing over the massive Himalayan mountain range — a similar intense climb could kill a human without lengthy acclimatisation. The geese make the journey on their annual spring migration from India to Central Asia. The team followed the migrations of these geese every hour using GPS satellite tags, following capture of the birds in India and Mongolia, where they winter and breed, respectively. In the study published May 31, they show that the geese can make the long climb in a single flight and that, surprisingly, rather than waiting for potentially favorable and predictable wind conditions to help carry them up and over the Himalaya (as had been thought previously), they wait for the winds to die down, and then make the climb over the mountains in the relative calm and peace of the night and early morning.
The geese's summer habitat is high altitude lakes where the bird grazes on short grass. The species has been reported as migrating south from Siberia via the Qinghai lake region in China before its crossing of the Himalaya. The Bar-headed Goose is one of the world's highest flying birds, having been seen at up to 33,382 feet. It has a slightly larger wing area for its weight than other geese, which is believed to help the goose fly at high altitudes. Studies have found that they breathe more efficiently under low oxygen conditions and are able to reduce heat loss. The hemoglobin of their blood has a higher oxygen affinity than that of other geese.
The Bar-headed Goose migrates over the Himalayas to spend the winter in parts of India (from Assam to as far south as Tamil Nadu), Northern Burma and the wetlands of Pakistan. The bird can fly the 1000-mile migration route in just one day as it is able to fly in the jet stream.
"We think the geese may be essentially risk averse", said Dr Charles Bishop (Principal Investigator of the project), "with the calmer winds at night offering an extra degree of safety and helping to avoid storms. The birds may also find it easier to keep together and to fly in formation."
The earlier flight times in the cooler, denser, morning air could help the geese to avoid the heat load of flying during the hottest time of the day in India whilst performing their intense workout."We were amazed to see that the geese were maintaining these climbs for hours on end." said Dr Lucy Hawkes. "It seemed quite enough that they could cope with such intense exercise at altitude, let alone that they didn’t stop to take regular breaks during the climbs, which last for at least seven hours over the Himalaya".
Denser air will also improve the lift generated by the wings and reduce the overall cost of flying, while improving the amount of oxygen available to the birds. Studies of a similar bird, the Brent goose, while migrating between Ireland and Canada, have suggested that their ability to climb while flying is so poor that they may land and walk across the imposing Greenland ice cap rather than maintaining flight! This makes the migration of the bar-headed goose seem even more remarkable.
At 18,000 feet atmospheric pressure and, therefore, oxygen density and availability, is only half of that at sea level. Near the top of Mount Everest, conditions can be even more inhospitable, with temperatures well below zero and the partial pressure of oxygen reduced to only a third of that at sea level. Humans struggle even to walk above 23,000 feet, so it seems incredible that these large geese may be able to sustain flapping flight at these heights.
For further information: http://www.bangor.ac.uk/research/full.php.en?nid=4691&tnid=0
Photo: image credit Nyanbayar Batbayar