Abstract Research aimed at understanding the evolution of costly, seemingly altruistic helping behaviour in cooperative birds has strongly focused on a single aspect of helping—offspring provisioning. However, various other activities are also important for successful breeding, most notably nest defence, and emphasis on a single aspect of helping might hamper a full understanding of the evolutionary drivers of cooperation and seemingly altruistic helping behaviour. Nonetheless, the extent to which social classes (i.e. dominant breeders and subordinate helpers), as well as different individuals within social classes, divide tasks in cooperative groups remains largely unknown. Here we tested whether individual purple-crowned fairy-wrens, Malurus coronatus , show task division in the two forms of costly offspring care important for reproductive success: nestling provisioning and nest defence (to predator models presented at nests). Subordinates and breeders generally contributed to both tasks. Breeders defended marginally more than subordinates, and provisioned at a consistently high level, irrespective of their individual contribution to defence, whereas subordinates’ investment in both types of care was positively correlated. Thus, we found no evidence for division of tasks between or within social classes, highlighting it may be absent in facultatively cooperative birds even when activities are costly and important for reproduction. This suggests that in such species, cooperative improvement of overall investment may be more effective than enhanced individual efficiency at different tasks. Significance statement In many social species, cooperation between individuals to achieve communal goals is important for successful reproduction. When multiple individuals are working together, division of tasks can occur, with tasks unevenly distributed among group members. Research on cooperative breeding, where subordinate helpers seemingly altruistically assist others in raising their young, has however mainly focused on offspring provisioning, while subordinates can often contribute to several breeding tasks. Thus, if task divisioning occurs, this would call into question conclusions about adaptive benefits of helping based on provisioning effort alone. Here we use nestling feeding watches and predator model presentations at nests to quantify nestling provisioning and nest defence effort by individuals in a classical cooperative breeder, the purple-crowned fairy-wren. We show a lack of task divisioning by breeders and subordinates, which is reassuring for our current understanding of the evolution of cooperative breeding.

中文翻译：

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合作鸟的巢穴防御和后代供应：个体下属的总贡献不同，但繁殖者和下属之间没有分工

摘要 旨在了解合作鸟类中代价高昂、看似无私的帮助行为的演变的研究强烈关注帮助的一个方面——提供后代。然而，各种其他活动对于成功繁殖也很重要，最显着的是筑巢防御，并且强调帮助的单一方面可能会妨碍对合作和看似无私的帮助行为的进化驱动因素的充分理解。尽管如此，社会阶层（即主导饲养者和从属帮手）以及社会阶层内的不同个体在合作团体中分工的程度仍然很大程度上未知。在这里，我们测试了个别紫冠仙鹪鹩、Malurus coronatus、展示对繁殖成功很重要的两种昂贵的后代护理形式的任务分工：雏鸟供应和巢穴防御（对于在巢穴中展示的捕食者模型）。下属和饲养员通常对这两项任务都有贡献。育种者比下属略多地进行防御，并且无论他们对防御的个人贡献如何，都始终保持高水平的供应，而下属对两种类型的护理的投资呈正相关。因此，我们没有发现社会阶层之间或内部的任务分工的证据，强调即使活动对繁殖来说成本高昂且重要，兼性合作的鸟类也可能不存在这种分工。这表明在此类物种中，整体投资的合作改进可能比不同任务中提高个体效率更有效。意义声明 在许多社会物种中，个体之间合作以实现共同目标对于成功繁殖很重要。当多个人一起工作时，可能会出现任务分工，任务在团队成员之间分布不均。关于合作育种的研究，下属助手似乎无私地帮助他人抚养他们的孩子，但主要集中在提供后代上，而下属通常可以参与多项育种任务。因此，如果发生任务划分，这将质疑关于仅基于供应工作的帮助的适应性好处的结论。在这里，我们在巢中使用雏鸟喂食手表和捕食者模型演示来量化经典合作育种者中个体的雏鸟供应和巢穴防御工作，紫冠仙鹪鹩。我们表现​​出缺乏育种者和下属的任务划分，这对我们目前对合作育种进化的理解令人放心。