Data from: Delayed dispersal and the costs and benefits of different routes to independent breeding in a cooperatively breeding bird

Why sexually mature individuals stay in groups as nonreproductive subordinates is central to the evolution of sociality and cooperative breeding. To understand such delayed dispersal, its costs and benefits need to be compared with those of permanently leaving to float through the population. However, comprehensive comparisons, especially regarding differences in future breeding opportunities, are rare. Moreover, extraterritorial prospecting by philopatric individuals has generally been ignored, even though the factors underlying this route to independent breeding may differ from those of strict philopatry or floating. We use a comprehensive predictive framework to explore how various costs, benefits and intrinsic, environmental and social factors explain philopatry, prospecting, and floating in Seychelles warblers (Acrocephalus sechellensis). Not only floaters more likely obtained an independent breeding position before the next season than strictly philopatric individuals, but also suffered higher mortality. Prospecting yielded similar benefits to floating but lower mortality costs, suggesting that it is overall more beneficial than floating and strict philopatry. While prospecting is probably individual-driven, although limited by resource availability, floating likely results from eviction by unrelated breeders. Such differences in proximate and ultimate factors underlying each route to independent breeding highlight the need for simultaneous consideration when studying the evolution of delayed dispersal.

性成熟个体为何仍以非繁殖从属者的身份留在群体中，是社会性（sociality）与合作繁殖（cooperative breeding）演化的核心议题。为阐释此类延迟扩散现象，需将其成本与收益，与永久离开群体、在种群中漫游以寻求繁殖机会的成本与收益进行对比。然而，相关的全面对比研究较为匮乏，尤其是针对未来繁殖机会差异的研究。此外，具备恋群性（philopatry）的个体所开展的领地外探查（extraterritorial prospecting）行为，此前通常被忽视——尽管通过该途径实现独立繁殖的背后驱动因素，可能与严格恋群或漫游繁殖存在差异。本研究采用全面的预测框架，探究各类成本、收益以及内在、环境与社会因素，如何解释塞舌尔莺（Acrocephalus sechellensis）的恋群、领地外探查与漫游繁殖行为。研究结果表明，漫游个体不仅比严格恋群个体更易在下一个繁殖季前获得独立繁殖位，其死亡率也更高。领地外探查的收益与漫游繁殖相似，但死亡率成本更低，这意味着该策略整体上比漫游繁殖与严格恋群更具优势。尽管领地外探查可能由个体自身驱动，但受资源可获得性限制；而漫游繁殖大概率源于与繁殖者无亲缘关系的个体的驱逐。各类独立繁殖途径背后的近因与远因差异，凸显了在研究延迟扩散演化时，需同时综合考量这些因素的必要性。