Control of the onset of nocturnal migration

夜间迁徙的候鸟在繁殖区和越冬区之间没有社会指引。为了到达正确的地点和时间，它们天生的迁徙程序定义了鸟类迁徙的时空组织和它们对环境线索的典型反应。当鸟类在迁徙期间被关在笼子里时，它们表现出夜间活动，称为迁徙不安。迁徙不安的时间模式和强度是内源性控制的。然而，光周期、温度和身体状况的变化调节了季节模式。这些因素也会影响移民在中途停留点的离境概率。尽管通过鸟笼实验和对野生鸟类的跟踪（无线电遥测、雷达、稳定同位素等），我们已经很好地研究了候鸟的年周期和昼夜节律以及实现的迁徙行为，但我们对以下方面的信息知之甚少：(1)夜间迁徙不安的确切开始时间和夜间迁徙的开始时间；(2)这两种特征是否具有时间相关性；（iii）受到强烈的内源性控制；（iv）外源性因素对这两种性状的发生时间有重大影响。然而，这方面的知识对于认识造成迁移的一般时间和最近观察到的迁移时间变化的机制是必不可少的。夜间迁徙的开始决定了夜间潜在的飞行范围。每晚所有潜在飞行范围的季节性总和影响迁徙的总速度，进而影响迁徙的总时间。因此，为了了解鸟类迁徙，有必要研究哪些内源性和外源性因素显著影响夜间迁徙的开始。通过结合笼子实验来确定夜间迁徙不安的开始和无线电遥测来确定同一个体夜间迁徙的开始，我将(I)描述这两种特征的时间模式，（ii）找出这两种特征是否在时间上相互关联，并确定（iii）内源性和（iv）外源性因素如何影响这两种特征在夜间的时间。为此，北方小麦（Oenanthe Oenanthe）将在黑尔戈兰被捕获。由于岛屿面积小，可以精确地确定无线电标记鸟类的存在和不存在。在迁徙中，斯堪的纳维亚的提名形式繁殖和岛上，格陵兰岛和加拿大的leucorhoa亚种繁殖经常发生在黑尔戈兰。由于所有的北方小麦都在萨赫勒以南的非洲过冬，种群在不同的繁殖地区有不同的总迁徙距离，春季从黑尔戈兰的剩余迁徙距离不同，而秋季则没有。该框架允许在总迁移距离（内源因素）、剩余迁移距离、光周期、季节日期、温度、身体状况和天气（所有外源因素）方面测试两种性状的差异。

Nocturnal migrants travel without social guidance between the breeding and wintering areas. To arrive at the correct place and time, their innate migration program defines birds` spatiotemporal organisation of migration and their typical reactions to environmental cues. When birds are kept in cages during migration, they show nocturnal activity, called migratory restlessness. The temporal pattern and intensity of migratory restlessness is endogenously controlled. However, changes in photoperiod, temperature and body condition modulate the seasonal pattern. These factors also influence the departure probability of a migrant at a stopover site. Although the circannual and circadian rhythms in migrants and the realised migration behaviour are well studied by cage experiments and tracking of wild birds (radio telemetry, radar, stable isotopes, etc.), we have little information (i) about the exact start of nocturnal migratory restlessness and onset of nocturnal migration within the night, (ii) whether both traits are temporally related, (iii) are strongly endogenous controlled and (iv) which exogenous factors significantly influence the timing of both traits. Knowledge about this is, however, essential for recognizing the mechanisms responsible for the general timing of migration and for the recently observed temporal change in migration. Onset of nocturnal migration defines the potential flight range per night. The seasonal sum of all potential flight ranges per night influences total speed of migration which in turn affects the overall timing of migration. For our understanding of bird migration it is hence essential investigating which endogenous and exogenous factors influence significantly the onset of nocturnal migration. By combining cage experiments to determine the start of nocturnal migratory restlessness and radio telemetry to identify the onset of nocturnal migration for the same individual I will (i) describe the temporal pattern of both traits, (ii) find out whether both traits correlate temporally with each other and identify how (iii) endogenous and (iv) exogenous factors influence the timing of both traits within the night. To this end, Northern Wheatears (Oenanthe oenanthe) will be caught on Helgoland. Due to the small size of the island presence and absence can be precisely determined for radio-tagged birds. On migration the nominate form breeding in Scandinavian and the leucorhoa subspecies breeding on Island, Greenland and in Canada occur regularly on Helgoland. As all Northern Wheatears winter in sub-Sahelian Africa, populations have depending on their breeding areas different total migration distances, different remaining migration distances from Helgoland in spring but not in autumn. This framework allows testing differences in both traits in respect of total migration distance [endogenous factor], remaining migration distance, photoperiod, date of season, temperature, body condition and weather [all exogenous factors].