Abstract 

Cooperative breeding sometimes occurs when adult breeders form groups following natal dispersal and mating. In such cases, individuals typically face a choice of social partner with whom to cooperate. Selecting appropriate social partners is crucial to maximising the fitness payoffs from cooperation, but our understanding of the criteria guiding partner choice is limited. Here, we analyse helping decisions by long-tailed tits (Aegithalos caudatus), which may redirect their care to assist breeders in raising offspring following the failure of their own nests. In this species, helpers prefer to help relatives at nearby nests, but it is unclear whether other criteria that may affect helper fitness also influence helping decisions. When choosing among broods of equivalent kinship, we found that helpers did not prefer those broods that offered the greatest indirect fitness returns. Further analyses revealed that helpers did not choose nests on the basis of brood size or age, but were more likely to help broods that were closer to their own failed nests and that were already being cared for by other helpers. Both effects likely reflect the limited choice available to helpers: although individuals breed close to relatives within kin neighbourhoods, a high rate of nest predation constrains helpers’ choice of broods. In other species where cooperatively breeding groups form after natal dispersal, a greater range of options may be available and here detailed analysis of group formation will be helpful for determining the decision rules that underpin partner choice and permit stable cooperation in the face of alternative options.

Significance statement

Cooperative breeding occurs most frequently when offspring delay dispersal from their natal site and help to care for their younger siblings. In some species, however, individuals first disperse and then come together as adults to cooperate in rearing young. In the latter case, multiple social partners may be available — what then determines which partner is helped? We studied partner choice in long-tailed tits, which may help to feed other broods if their own brood fails. When multiple related broods were available, individuals were more likely to help those close by but showed no preference for broods offering the greatest indirect fitness returns. One explanation for this result is that helping options for most individuals are limited by high levels of nest predation, favouring a simpler decision-making process based on identifying close relatives breeding in close proximity.

中文翻译：

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谁来帮助？通过重定向护理帮助合作繁殖鸟类的决策

摘要 

当成年育种者在出生后分散和交配后形成群体时，有时会发生合作育种。在这种情况下，个人通常面临选择与之合作的社会伙伴。选择合适的社会伙伴对于最大化合作的适应度回报至关重要，但我们对指导伙伴选择的标准的理解是有限的。在这里，我们分析了长尾山雀（Aegithalos caudatus)，这可能会重定向他们的照顾，以帮助育种者在自己的巢穴失败后抚养后代。在这个物种中，助手更喜欢帮助附近巢穴的亲戚，但尚不清楚可能影响助手适应性的其他标准是否也会影响帮助决定。在同等亲属关系的群体中进行选择时，我们发现帮助者并不喜欢那些提供最大间接适应度回报的群体。进一步的分析表明，帮助者不会根据巢的大小或年龄来选择巢穴，而是更有可能帮助那些离自己失败的巢更近并且已经被其他帮助者照顾的巢。这两种影响可能都反映了帮助者的选择有限：尽管个人在近亲附近繁殖，巢穴捕食率高限制了助手对育雏的选择。在其他物种，在出生分散后形成合作繁殖群体，可能会有更大范围的选择，这里对群体形成的详细分析将有助于确定支持伙伴选择的决策规则，并在面对替代选择时允许稳定合作。

意义陈述

当后代延迟从出生地分散并帮助照顾他们的弟弟妹妹时，合作繁殖最常发生。然而，在某些物种中，个体首先分散，然后成年后聚集在一起合作抚养幼崽。在后一种情况下，可能有多个社会伙伴可用——那么是什么决定了哪个伙伴得到帮助？我们研究了长尾山雀的伴侣选择，如果他们自己的巢穴失败，这可能有助于喂养其他巢穴。当有多个相关的育雏可用时，个体更有可能帮助附近的人，但对提供最大间接适应度回报的育雏没有表现出偏好。对这一结果的一种解释是，大多数人的帮助选择受到高水平的巢穴捕食的限制，