SOARING BEHAVIOR AND PERFORMANCE OF SOME EAST AFRICAN BIRDS, OBSERVED FROM A MOTOR-GLIDER
SOARING BEHAVIOR AND PERFORMANCE OF SOME EAST AFRICAN BIRDS, OBSERVED FROM A MOTOR-GLIDER
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DOI：
10.1111/j.1474-919x.1972.tb02603.x
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发表时间：
1972-01-01
期刊：
影响因子：
2.1
通讯作者：
PENNYCUICK, CJ
中科院分区：
文献类型：
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作者：
PENNYCUICK, CJ
在坦桑尼亚的塞伦盖蒂国家公园上空，人们乘坐电动滑翔机跟踪观察各种飞翔的鸟类。本文概述了研究区热对流的特点，并对两种兀鹫Gypus的食腐作用进行了研究。它们没有领土意识，在杀戮时大量聚集。在养育幼鸟时，它们可能会因猎物的移动而被迫在离巢很远的地方觅食。它们的越野性能足以在旱季条件下超过100公里的觅食半径。他们与斑点鬣狗竞争的能力被认为部分取决于这个因素，部分取决于提前到达杀戮的优势。这两种秃鹫似乎更多地通过观察其他秃鹫来寻找食物，而不是直接寻找食物。拉佩面秃鹫和白色头秃鹫被认为是定居的，并且依赖于对固定觅食区域的彻底搜索，而不是跟随迁徙的猎物。它们的翼载比吉普赛秃鹫低，而且没有被看到越野飞行。他们从不聚集在一起。冠鹫是一种独居的鸟类，但它确实会飞越整个国家，也会聚集在一起捕杀猎物。秃鹫单独翱翔，似乎善于利用热街等现象。它们不成群迁徙。黄褐色鹰和武鹰对滑翔机反应积极，并被怀疑将其视为潜在的猎物。白色鹳在欧洲和非洲之间迁徙，也通过热滑翔在东非境内旅行。它们成群结队地飞翔，不像秃鹫，它们依靠协调的社会行为来定位热气流。在选择路线时，他们往往对明显的天气标志反应迟钝。它们在热融时从底部进入积云，但可能不会爬到云底以上很远的地方。鹳单独飞翔，但有时也会成群飞行。在这样做的时候，它们的横向扩散比白色鹳要少，这降低了群体作为寻找热量单位的有效性;另一方面，它们似乎确实会对可见的天气信号做出反应，比如秃鹫或滑翔机飞行员。白色鹈鹕通过热飞翔在裂谷的不同湖泊之间旅行，表现出最高度协调的社会飞翔行为。与白色鹳不同的是，它们即使在盘旋时也是编队飞行的。当滑翔机接近时，鹳和鹈鹕比秃鹫或猛禽表现出更多的惊慌。这可能是由于它们在飞行中被捕食，例如被武鹰。概述了传统的热越野飞行的基础，并解释了为什么吉普赛秃鹫的高翼载适合于它们的漫游习惯。本文讨论了一种不绕圈热滑翔的方法，并证明这种方法对小型鸟类比大型鸟类更可行。鸟类和滑翔机飞行员在滑翔技术上的一些差异，在这个计算的光解释。黑鸢显然是利用这种技术在随机湍流中翱翔的。通过热滑翔可达到的越野速度应该与大型和小型鸟类在动力下的巡航速度相似。对能量消耗的粗略计算表明，一只大鸟（白色鹳）应该通过翱翔而不是在动力下飞行来减少23倍的燃料消耗，而对于一只小鸟（博内利莺）来说，这个因素只有2-4。还指出了为什么热滑翔对大型鸟类是一种有利的旅行手段而对小型鸟类不是的其他原因。
Various species of soaring birds were studied by following them in a motor‐glider, mainly over the Serengeti National Park, Tanzania. The characteristics of thermal convection in the study area are described in general terms.The two vulture species of the genusGypslive by scavenging among the herds of migratory ungulates, especially Wildebeest. They are not territorial, and gather in large numbers on kills. When raising young they may be obliged by game movements to forage at long distances from their nests. Their cross‐country performance is adequate for a foraging radius of over 100 km in dry‐season conditions. Their ability to compete with Spotted Hyaenas is thought to depend partly on this factor and partly on an advantage in arriving early at kills. These two species appear to find food more by watching other vultures than by searching for it directly.The Lappet‐faced and White‐headed Vultures are thought to be sedentary, and to depend on thorough searching of a fixed foraging territory, rather than on following migratory game. They have lower wing loadings than theGypsvultures, and were not seen cross‐country flying. They never gather in large numbers. The Hooded Vulture is a solitary nester, but it does fly across country, and does gather at kills. Vultures soar individually, and seem to be good at exploiting such phenomena as thermal streets. They do not travel in flocks.Tawny and Martial Eagles react positively to the glider, and are suspected of regarding it as potential prey.White Storks migrate between Europe and Africa, and also travel about within East Africa, by thermal soaring. They soar in flocks, and unlike vultures rely on co‐ordinated social behaviour to locate thermals. In choosing their route, they often fail to react to obvious weather signs. They enter cumulus clouds from the bottom when thermalling, but probably do not climb far above cloudbase.Marabou Storks soar individually, but also sometimes travel in flocks. When doing so, they show less lateral spreading than White Storks, which reduces the effectiveness of the flock as a thermal‐finding unit; on the other hand, they do seem to react to visible weather signs, like vultures or glider pilots.White Pelicans, which travel by thermal soaring between different lakes in the Rift Valley, show the most highly co‐ordinated social soaring behaviour. Unlike White Storks, they fly in formation even when circling.Storks and pelicans showed more signs of alarm when approached by the glider than did the vultures or birds of prey. This could be due to their being preyed upon in flight, for instance by Martial Eagles.The basis of conventional thermal cross‐country flying is outlined, and it is explained why the high wing loadings of theGypsvultures are appropriate to their peripatetic habits. A method of thermal soaring without circling is discussed, and shown to be more readily feasible for small than for large birds. Some differences in soaring techniques between birds and glider pilots are interpreted in the light of this calculation. A case in which Black Kites apparently used this technique to soar in random turbulence is described.The cross‐country speed attainable by thermal soaring should be similar to the cruising speed under power in both large and small birds. Rough calculations of the energy costs suggest that a large bird (White Stork) should reduce its fuel consumption by a factor of 23 by soaring rather than flying under power, whereas this factor would be only 2–4 for a small bird (Bonelli's Warbler). Other reasons why thermal soaring is an advantageous means of travel for large but not for small birds are also indicated.