Data from: Identifying drivers of breeding success in a long-distance migrant using structural equation modelling

In migrant animals, conditions encountered at various times and places throughout their annual cycle may affect breeding success. Yet, most studies so far have only investigated the effect of specific parts of the annual cycle, despite the importance to understand how different stages can interact and how these stages compare to intrinsic quality to properly modulate breeding success. Using a structural equation modelling approach, we investigated drivers of breeding success (migration cycle, individual quality, breeding conditions) in hoopoes (Upupa epops), a long-distant migrant. Our causal framework explained 75% of the variation in breeding success. The effect of the migration schedule was negligible, whereas the previous breeding attempt strongly influenced current breeding success. We suggest that the interplay of individual quality and environmental conditions during both previous and current breeding season may be more important drivers of breeding success than migration schedules, even in a long-distance migrant. We conclude that structural equation modeling is a promising tool to investigate causal relationships. Applied to hoopoes, we demonstrated that current breeding success is strongly linked to previous breeding success. Complementary analysis integrating weather and climate conditions during migration and the breeding season may provide a deeper and wider overview of the annual cycle of hoopoes and additional insights into the existence of carry-over effects in breeding success.

在迁徙动物中，其全年周期内不同时间与地点所遭遇的各类环境条件，均可能对繁殖成功率产生影响。然而迄今为止，绝大多数相关研究仅探讨了年度周期中特定阶段的效应，尽管厘清不同阶段如何相互作用、以及这些阶段与个体内在品质在调控繁殖成功率中的相对重要性，具有重要的科学意义。
本研究以长途迁徙鸟类戴胜（Upupa epops）为研究对象，采用结构方程模型（structural equation modelling）方法，探究了繁殖成功率的三类驱动因子：迁徙周期、个体品质与繁殖条件。我们构建的因果框架解释了75%的繁殖成功率变异。分析结果显示，迁徙节律对繁殖成功率的影响可忽略不计，而此前的繁殖尝试对当前繁殖成功率具有极强的调控作用。
我们认为，相较于迁徙节律，个体品质与前、当前繁殖季的环境条件之间的相互作用，或许是繁殖成功率更关键的驱动因子，即便对于长途迁徙物种而言亦是如此。
综上，结构方程模型是探究生态因果关系的极具潜力的研究工具。将其应用于戴胜的研究中，我们证实当前繁殖成功率与此前的繁殖尝试密切相关。后续可开展补充分析，整合迁徙与繁殖季的天气及气候条件，从而更全面深入地解析戴胜的年度周期，并进一步揭示繁殖成功率中遗留效应（carry-over effects）的存在规律。