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导。为了到达正确的地点和时间，鸟类与生俱来的迁徙计划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。当鸟类在迁徙过程中被关在笼子里时，它们会表现出夜间活动，称为迁徙躁动。迁徙躁动的时间模式和强度是由内源性控制的。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地点离开的概率。尽管通过笼养实验和对野生鸟类的跟踪(无线电遥测、雷达、稳定同位素等)很好地研究了候鸟的昼夜和昼夜节律以及实现的迁徙行为，但我们对以下几个方面的信息很少：(I)关于夜间迁徙躁动和夜间迁徙的确切开始，(Ii)这两个特征是否在时间上相关，(Iii)是强烈的内源控制的，以及(Iv)哪些外源因素显著影响这两个特征的时间。然而，这方面的知识对于认识到造成一般移徙时间和最近观察到的移徙时间变化的机制是至关重要的。夜间迁徙的开始决定了每晚的潜在飞行范围。每晚所有可能飞行范围的季节性总和影响迁徙的总速度，进而影响迁徙的整体时间。因此，研究哪些内源性和外源性因素对鸟类夜间迁徙的开始有重要影响，对于我们理解鸟类的迁徙是至关重要的。通过结合笼养实验来确定夜间迁徙躁动的开始，以及无线电遥测来确定同一个体夜间迁徙的开始，I将(I)描述这两个性状的时间模式，(Ii)找出这两个性状是否在时间上彼此相关，并确定(Iii)内源和(Iv)外源因素如何影响两个性状在夜间的时间。为此，将在赫尔戈兰捕获北方小麦(Oenanthe Oenanthe)。由于岛的面积很小，可以准确地确定无线电标记鸟类的存在和不存在。在迁徙上，斯堪的纳维亚人的命名形式繁殖以及在岛屿、格陵兰和加拿大的白鲸亚种繁殖在赫尔戈兰岛上定期发生。由于所有北方小麦都在萨赫勒以南非洲越冬，种群根据其繁殖区的不同有不同的总迁徙距离，春季与赫尔戈兰的剩余迁徙距离不同，但秋季不同。这一框架允许测试两个性状在总迁徙距离[内源因素]、剩余迁徙距离、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].