Abstract：
In migratory animals, the developmental period from inexperienced juveniles to breeding adults could be a key life stage in shaping population migration patterns. Nevertheless, the development of migration routines in early life remains underexplored. While age-related changes in migration routes and timing have been described in obligate migrants, most investigations into the ontogeny of partial migrants only focused on age-dependency of migration as a binary tactic (migrant or resident), and variations in routes and timing among individuals classified as \'migrants\' is rarely considered. To fill this gap, we study the ontogeny of migration destination, route and timing in a partially migratory red kite (Milvus milvus) population. Using an extensive GPS-tracking dataset (292 fledglings and 38 adults, with 1-5 migrations tracked per individual), we studied how nine different migration characteristics changed with age and breeding status in migrant individuals, many of which become resident later in life. Individuals departed later from and arrived earlier at the breeding areas as they aged, resulting in a gradual prolongation of stay in the breeding area by 2 months from the first to the fifth migration. Individuals delayed southward migration in the year prior to territory acquirement, and they further delayed it after occupying a territory. Migration routes became more direct with age. Individuals were highly faithful to their wintering site. Migration distance shortened only slightly with age and was more similar among siblings than among unrelated individuals. The large gradual changes in northward and southward migrations suggest a high degree of plasticity in temporal characteristics during the developmental window. However, the high wintering site fidelity points towards large benefits of site familiarity, prompting spatial migratory plasticity to be expressed through a switch to residency. The contrasting patterns of trajectories of age-related changes between spatial and temporal migration characteristics might reflect different mechanisms underlying the expression of plasticity. Investigating such patterns among species along the entire spectrum of migration tactics would enable further understanding of the plastic responses exhibited by migratory species to rapid environmental changes.
摘要：
在迁徙动物中，从没有经验的青少年到繁殖的成年人的发育期可能是塑造人口迁移模式的关键生命阶段。然而，早期迁移程序的发展仍未得到充分探索。虽然在义务移民中描述了与年龄相关的移民路线和时间变化，大多数对部分移民的个体发育的调查仅集中在移民的年龄依赖性上，这是一种二元策略（移民或居民），很少考虑被归类为“移民”的个人之间的路线和时间差异。为了填补这个空白，我们研究迁徙目的地的个体发育，部分迁徙的红色风筝（Milvusmilvus）种群的路线和时间。使用广泛的GPS跟踪数据集（292个雏鸟和38个成年人，每个人跟踪1-5次迁移)，我们研究了九种不同的迁徙特征如何随年龄和繁殖状况而变化，其中许多人在以后的生活中成为居民。随着年龄的增长，个人离开繁殖区的时间较晚，到达繁殖区的时间也较早，导致从第一次到第五次迁徙，在繁殖区的停留时间逐渐延长2个月。个人在获得领土的前一年推迟了向南迁移，他们在占领领土后进一步拖延了。随着年龄的增长，迁移路线变得更加直接。个人对他们的越冬地点非常忠诚。随着年龄的增长，迁移距离仅略有缩短，兄弟姐妹之间的迁移距离比无关个体之间的迁移距离更相似。向北和向南迁移的大量逐渐变化表明，在发育窗口期间，时间特征具有高度的可塑性。然而,较高的越冬地点保真度表明了地点熟悉度的巨大好处，促使空间迁移可塑性通过转换为居住区来表达。时空迁移特征之间与年龄相关的变化轨迹的对比模式可能反映了可塑性表达的不同机制。在整个迁徙策略范围内研究物种之间的这种模式，将能够进一步了解迁徙物种对快速环境变化表现出的可塑性反应。
