Swiss Ornithological Institute, Sempach, Switzerland.
Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
J Anim Ecol. 2024 Sep;93(9):1316-1327. doi: 10.1111/1365-2656.14150. Epub 2024 Jul 28.
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.
在迁徙动物中，从无经验的幼体到繁殖成体的发育阶段可能是塑造种群迁徙模式的关键生命阶段。然而，早期生命中迁徙习惯的发展仍然未被充分探索。虽然在强制性迁徙动物中已经描述了与年龄相关的迁徙路线和时间变化，但大多数对部分迁徙动物个体发育的研究仅关注于将迁徙作为二元策略（迁徙者或留居者）的年龄依赖性，而很少考虑个体之间迁徙路线和时间的变化。为了填补这一空白，我们研究了部分迁徙红风筝（Milvus milvus）种群的迁徙目的地、路线和时间的个体发育。使用广泛的 GPS 跟踪数据集（292 只幼鸟和 38 只成年鸟，每个个体跟踪 1-5 次迁徙），我们研究了在迁徙个体中，随着年龄和繁殖状态的变化，九个不同的迁徙特征如何变化，其中许多个体在以后的生活中成为留居者。个体随着年龄的增长，离开繁殖地的时间越来越晚，到达繁殖地的时间越来越早，导致第一次到第五次迁徙期间，在繁殖地停留的时间逐渐延长了 2 个月。个体在获得领地之前的前一年会延迟向南迁徙，在占据领地后会进一步延迟。随着年龄的增长，迁徙路线变得更加直接。个体对越冬地高度忠诚。迁徙距离仅随年龄略有缩短，而且兄弟姐妹之间比非亲缘个体之间更为相似。北迁和南迁的大幅逐渐变化表明，在发育窗口期，时间特征具有高度的可塑性。然而，高越冬地忠诚度表明，对栖息地熟悉度的好处很大，促使通过转为留居者来表现空间迁徙的可塑性。与年龄相关的变化的空间和时间迁徙特征的轨迹之间的相反模式可能反映了表达可塑性的不同机制。在整个迁徙策略谱中，对物种之间的这种模式进行调查将有助于进一步了解迁徙物种对快速环境变化表现出的弹性反应。
