The world's highest flying bird
Lucy Hawkes, from University of Exeter, UK, will give a talk about "On a wild goose chase for the world's highest flying bird".
Many of the most spectacular migrations on earth are made by birds. One notable example is the bar-headed goose, renowned for migratory flights at extremely high altitudes over the world’s tallest mountains, the Himalayas, where partial pressure of oxygen is dramatically reduced while flight costs, in terms of rate of oxygen consumption, are greatly increased. By tracking 91 geese, we show that these birds typically travel through the valleys of the Himalayas and not over the summits, with maximum flight altitudes of 7290 m, but with 95 per cent of locations received from less than 5489 m. Populations of geese that winter at sea level in India are capable of passing over the Himalayas in less than a day, typically climbing between 4,000 and 6,000min 7–8 h. Surprisingly, these birds do not rely on the assistance of upslope tailwinds that usually occur during the day and can support minimum climb rates of 0.8–2.2 km·h-1, even in the relative stillness of the night. Bar-headed geese have a suite of adaptations for high altitude throughout the oxygen transport cascade, manifest in an ability of these birds to run at maximum speeds (determined in normoxia) for 15 minutes in severe hypoxia (7% O2; simulating 8500 m altitude) with no decrease in arterial blood oxygen saturation. Barnacle geese (n = 10), on the other hand, were unable to complete similar trials in severe hypoxia. Further, using implanted loggers that recorded heart rate, acceleration, pressure, and temperature, we found no evidence of training for migration in bar-headed geese in advance of migration. It would seem, therefore, that bar-headed geese are capable of sustained climbing flight over the passes of the Himalaya under their own aerobic power.