Migration behaviour of long- and medium-distance songbird migrants

鸟类可以区分居民和兼职和义务候鸟，尽管这些类别并不明显，它们的极端设置在一个连续统一体的不同末端。在古北区-非洲迁徙系统中，迁徙被分为跨越撒哈拉的迁徙，即在撒哈拉以南越冬的物种，表现出较长的季节性迁徙周期(长途迁徙)和较北越冬的物种(中程迁徙)。由于我们目前缺乏关于这两个移民群体可能不同的移民战略的基本信息，我们缺乏有用的解释，解释为什么长途移民因气候变化而发生的季节性物候变化不同于中途移民。尽管有几项研究考察了这两类单一物种的迁徙行为，但到目前为止，还没有研究通过使用实验方法和在自由飞行条件下同时联合考虑这两类物种的迁徙行为来调查它们迁徙行为的潜在差异。最优迁移理论预测，与长途移民相比，中途移民有更多的时间进行季节性流动。因此，前者预计会有更多的出行时间，以最大限度地减少能源消耗。相比之下，长途移民应该最大限度地提高移民速度，以便及时到达更远的目的地。由于更长的迁徙距离在时间和精力上都更昂贵，长途迁徙在其他生活史特征上的时间和精力更少，如繁殖、蜕皮和越冬。因此，与较短的迁徙路线相比，较大的选择压力将作用于迁徙路线较长的物种。在长途移民的生活史事件的季节性时间组织中观察到的小程度的表型变异被假设为来自低水平的可遗传变异。在这里，我建议使用四个可比较的研究物种来批判性地研究长途和中途迁徙的迁徙行为。为了做到这一点，我将结合笼子实验和赫尔戈兰岛上自由飞行的鸟类的研究，这些实验涉及暂时被限制的候鸟，环境条件可以控制。为了估计自由飞行鸟类的迁徙行为，我计划在赫尔戈兰岛上现有的遥测站之外，建立一个大规模的自动数字遥测阵列。有了这个系统，鸟类在德国湾大片地区和邻近沿海地区的活动将被覆盖。这将是第一次采用整体方法，从长途和短途移徙者的迁徙行为(时间与精力)及其对春季和秋季迁徙期间环境变化的反应规范范围两方面论证不同的解决办法。

Birds can be distinguished between residents and facultative and obligate migrants, although these categories are not distinct, and their extremes are set at different ends of a continuum. Within the Palaearctic-African migration system, migrants are separated into trans-Saharan migrants, i.e., species that winter south of the Sahara, which show longer seasonal migration periods (long-distance migrants), and those that winter farther north (medium-distance migrants). Due to our current lack of fundamental information about the potentially different migration strategies of these two migration groups, we lack useful explanations of why the changes in the seasonal phenology of long-distance migrants that occurred in response to changes in climate differed from those of medium-distance migrants. Although several studies have examined the migration behaviour of single species of both of these groups, to date, no study has investigated potential differences in their migration behaviour by jointly considering species of both groups at the same time using an experimental approach and under free-flying conditions. Optimal migration theory predicts that medium-distance migrants have more time for their seasonal movements than long-distance migrants. Therefore, the former is predicted to have more time for travelling to minimize energy expenditure. In contrast, long-distance migrants are supposed to maximize the speed of migration to reach their more distant destinations in time. Because longer migration distances are more costly in terms of time and energy, long-distance migrants have less time and energy for other life history traits, i.e., breeding, moulting, and wintering. Therefore, stronger selection pressure is predicted to act on species with longer migration routes compared with those with shorter routes. The small degree of phenotypic variation that has been observed in the seasonal temporal organization of life-history events in long-distance migrants was hypothesized to come from low levels of heritable variation. Here, I propose to critically study the migration behaviour of long- and medium-distance migrants using four comparable study species. To do so, I will combine cage experiments involving temporarily confined migrants, for which environmental conditions can be controlled, with studies of free-flying birds on Helgoland. To estimate the migration behaviour of free-flying birds, I plan to set up a large-scale automated digital telemetry array in addition to the existing telemetry station on Helgoland. With this system, birds' movements across large parts of the German Bight and the adjacent coastal areas would be covered. This would be the first study to demonstrate, using a holistic approach, the different solutions found by selection for long- and short-distance migrants in terms of both their migration behaviour (time vs. energy) and their range of reaction norms to environmental variation during both spring and autumn migration.