The paradox of extreme high-altitude migration in bar-headed geese Anser indicus
The paradox of extreme high-altitude migration in bar-headed geese Anser indicus
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DOI：
10.1098/rspb.2012.2114
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发表时间：
2013-01-07
影响因子：
4.7
通讯作者：
Bishop, C. M.
中科院分区：
文献类型：
--
作者：
Hawkes, L. A.;Balachandran, S.;Bishop, C. M.
斑头雁以在世界上最高的山脉喜马拉雅山脉的极高海拔地区进行迁徙飞行而闻名，在那里，氧气分压急剧降低，而飞行成本，就氧气消耗率而言，大大增加。这种不匹配是自相矛盾的，也不清楚为什么鹅会飞得比绝对必要的高。此外，缺乏对高空飞行的直接经验测量。我们测试了迁徙的斑头雁是否实际上降低了飞行高度，并利用有利的风来降低飞行成本。通过对91只鹅的追踪，我们发现这些鸟通常会穿过喜马拉雅山脉的山谷，而不是峰顶。我们报告了南行和北行鹅的最大飞行高度分别为7290米和6540米，但95%的地点收到的海拔低于5489米。大雁沿着比大圈（最短距离）路线长112公里的路线飞行，过境地面速度表明它们很少受益于顺风。来自东部的斑头雁通常只在它们下面的地形所要求的高度飞行，很少在有利的风中飞行。然而，在人类和其他哺乳动物只能在远低于海平面最高点的地方活动的情况下，它们的迁徙代表了一个巨大的挑战。
Bar-headed geese are 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. Such a mismatch is paradoxical, and it is not clear why geese might fly higher than is absolutely necessary. In addition, direct empirical measurements of high-altitude flight are lacking. We test whether migrating bar-headed geese actually minimize flight altitude and make use of favourable winds to reduce flight costs. By tracking 91 geese, we show that these birds typically travel through the valleys of the Himalayas and not over the summits. We report maximum flight altitudes of 7290 m and 6540 m for southbound and northbound geese, respectively, but with 95 per cent of locations received from less than 5489 m. Geese travelled along a route that was 112 km longer than the great circle (shortest distance) route, with transit ground speeds suggesting that they rarely profited from tailwinds. Bar-headed geese from these eastern populations generally travel only as high as the terrain beneath them dictates and rarely in profitable winds. Nevertheless, their migration represents an enormous challenge in conditions where humans and other mammals are only able to operate at levels well below their sea-level maxima.