Rotics Shay, Kaatz Michael, Resheff Yehezkel S, Turjeman Sondra Feldman, Zurell Damaris, Sapir Nir, Eggers Ute, Flack Andrea, Fiedler Wolfgang, Jeltsch Florian, Wikelski Martin, Nathan Ran
Department of Ecology, Evolution and Behavior, Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 91904, Jerusalem, Israel.
Vogelschutzwarte Storchenhof Loburg e.V., Chausseestr. 18, D-39279, Loburg, Germany.
J Anim Ecol. 2016 Jul;85(4):938-47. doi: 10.1111/1365-2656.12525. Epub 2016 May 19.
Migration conveys an immense challenge, especially for juvenile birds coping with enduring and risky journeys shortly after fledging. Accordingly, juveniles exhibit considerably lower survival rates compared to adults, particularly during migration. Juvenile white storks (Ciconia ciconia), which are known to rely on adults during their first fall migration presumably for navigational purposes, also display much lower annual survival than adults. Using detailed GPS and body acceleration data, we examined the patterns and potential causes of age-related differences in fall migration properties of white storks by comparing first-year juveniles and adults. We compared juvenile and adult parameters of movement, behaviour and energy expenditure (estimated from overall dynamic body acceleration) and placed this in the context of the juveniles' lower survival rate. Juveniles used flapping flight vs. soaring flight 23% more than adults and were estimated to expend 14% more energy during flight. Juveniles did not compensate for their higher flight costs by increased refuelling or resting during migration. When juveniles and adults migrated together in the same flock, the juvenile flew mostly behind the adult and was left behind when they separated. Juveniles showed greater improvement in flight efficiency throughout migration compared to adults which appears crucial because juveniles exhibiting higher flight costs suffered increased mortality. Our findings demonstrate the conflict between the juveniles' inferior flight skills and their urge to keep up with mixed adult-juvenile flocks. We suggest that increased flight costs are an important proximate cause of juvenile mortality in white storks and likely in other soaring migrants and that natural selection is operating on juvenile variation in flight efficiency.
迁徙带来了巨大的挑战，尤其是对于那些在羽翼初丰后不久就应对漫长而危险旅程的幼鸟来说。因此，与成年鸟类相比，幼鸟的存活率要低得多，尤其是在迁徙期间。已知幼年白鹳在首次秋季迁徙时依赖成年白鹳，大概是为了导航，其年存活率也远低于成年白鹳。我们利用详细的GPS和身体加速度数据，通过比较一岁幼鸟和成年白鹳，研究了白鹳秋季迁徙特性中与年龄相关差异的模式和潜在原因。我们比较了幼鸟和成年白鹳的运动、行为和能量消耗参数（根据总体动态身体加速度估算），并将其与幼鸟较低的存活率联系起来。幼鸟使用振翅飞行与翱翔飞行的比例比成年白鹳多23%，据估计在飞行过程中消耗的能量多14%。幼鸟在迁徙过程中没有通过增加觅食或休息来弥补较高的飞行成本。当幼鸟和成年白鹳在同一鸟群中一起迁徙时，幼鸟大多飞在成年白鹳后面，分开时就会被落下。与成年白鹳相比，幼鸟在整个迁徙过程中飞行效率的提高更大，这似乎至关重要，因为飞行成本较高的幼鸟死亡率增加。我们的研究结果表明，幼鸟较差的飞行技能与其跟上成年与幼年混合鸟群的冲动之间存在冲突。我们认为，飞行成本增加是白鹳幼鸟死亡的一个重要直接原因，其他翱翔类候鸟可能也是如此，并且自然选择作用于幼鸟飞行效率的差异。
