For migratory birds optimal timing of the onset of reproduction is vital, especially when suitable conditions for reproduction occur only for a short while during the year. With increasing latitude the suitable period becomes shorter and we expect the organization of annual cycle to be more synchronized to the local conditions across individuals of same population. This should result in low variation of arrival and departure date in breeding sites at higher latitudes. We quantify the temporal and geographical variation in pre‐ and post‐breeding migration between individuals from four different populations of alpine swifts Tachymarptis melba along a latitudinal gradient. We tracked 215 individuals in three years with geolocators. The two western and two eastern populations showed separate migratory flyways and places of residence in Africa. Length of stay at the breeding sites was negatively correlated with latitude and differed by more than a month between populations. Duration of migration was similarly short in all populations (median 6.2 days in autumn and 8.7 days in spring). However, variation in timing of migration was unrelated to latitude and individuals everywhere arrived in the same asynchrony at the breeding site.

中文翻译：

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特快跨撒哈拉移民的人口针对年度周期的特定调整

对于候鸟来说，最佳的繁殖开始时间至关重要，尤其是当一年中只有很短的繁殖条件时。随着纬度的增加，合适的时期将缩短，我们希望年周期的组织将与相同人口个体之间的当地条件更加同步。这将导致高纬度繁殖地点的到达和离开日期变化较小。我们对来自四个不同高山高寒种群Tachymarptis melba的个体之间的繁殖前和繁殖后迁移的时间和地理差异进行了量化沿着纬度梯度。我们在三年内通过地理定位器跟踪了215个人。西部的两个人口和东部的两个人口显示出不同的迁徙路线和非洲的居住地。在繁殖地点的停留时间与纬度呈负相关，并且种群之间的差异超过一个月。在所有人口中，迁徙的持续时间都同样较短（秋天平均为6.2天，春季平均为8.7天）。但是，迁徙时间的变化与纬度无关，各地的个体以相同的异步到达繁殖地点。