When and where does mortality occur in migratory birds? Direct evidence from long-term satellite tracking of raptors

1. Information about when and where animals die is important to understand population regulation. In migratory animals, mortality might occur not only during the stationary periods (e.g. breeding and wintering) but also during the migration seasons. However, the relative importance of population limiting factors during different periods of the year remains poorly understood, and previous studies mainly relied on indirect evidence. 2. Here we provide direct evidence about when and where migrants die by identifying cases of confirmed and probable deaths in three species of long-distance migratory raptors tracked by satellite telemetry. 3. We show that mortality rate was about six times higher during migration seasons than during stationary periods. However, total mortality was surprisingly similar between periods, which can be explained by the fact that risky migration periods are shorter than safer stationary periods. Nevertheless, more than half of the annual mortality occurred during m...

1. 了解动物死亡的时间与地点，对于阐明种群调控（population regulation）机制具有重要意义。对于迁徙动物而言，其死亡不仅可能发生在静止阶段（stationary periods，如繁殖与越冬期），也可能出现在迁徙季。然而，学界对一年中不同阶段的种群限制因子（population limiting factors）的相对重要性仍知之甚少，且既往研究主要依赖间接证据（indirect evidence）。2. 本研究针对通过卫星遥测（satellite telemetry）追踪的3种长距离迁徙猛禽（long-distance migratory raptors），识别其确认死亡与疑似死亡案例，以此直接揭示迁徙动物的死亡时间与地点信息。3. 研究结果显示，迁徙季的死亡率较静止阶段高出约6倍。但令人意外的是，两个阶段的年度总死亡率却较为相近，这可通过风险较高的迁徙期时长短于更安全的静止期这一事实得到合理解释。尽管如此，全年超过半数的年度死亡事件仍发生在m...