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.

为何性成熟个体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）演化研究的核心议题。为理解这类延迟扩散（delayed dispersal）现象，需将其成本与收益与永久离开群体、在种群中漫游的个体进行对比。然而，现有研究鲜有开展全面对比，尤其是在未来繁殖机会差异层面。此外，恋巢个体的域外勘探（extraterritorial prospecting）行为长期被忽视——尽管这条通往独立繁殖的路径背后的驱动因素，或与严格恋巢或漫游繁殖者截然不同。

我们采用一套全面的预测框架，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）中的恋巢、勘探与漫游行为。研究结果显示，漫游者不仅更有可能在下一个繁殖季前获得独立繁殖地位，同时还面临更高的死亡风险。域外勘探虽可获得与漫游相近的收益，却仅需承担更低的死亡成本，这表明整体而言，勘探行为比漫游与严格恋巢更具适应性优势。

尽管勘探行为大概率由个体自身驱动，但会受到资源可获得性的限制；而漫游行为则可能源于无亲缘关系繁殖者的驱逐。每种独立繁殖路径背后的近因（proximate factors）与终极因（ultimate factors）均存在差异，这凸显了在研究延迟扩散演化时，需同时考量各类因素的必要性。