Animals create diverse structures, both individually and cooperatively, using materials from their environment. One striking example are the nests birds build for reproduction, which protect the offspring from external stressors such as predators and temperature, promoting reproductive success. To construct a nest successfully, birds need to make various decisions, for example regarding the nest material and their time budgets. To date, research has focused mainly on species where one sex is primarily responsible for building the nest. In contrast, the cooperative strategies of monogamous species in which both sexes contribute to nest building are poorly understood. Here we investigated the role of both sexes in nest building and fitness correlates of behaviour in wild, monogamous jackdaw pairs (Corvus monedula). We show that both partners contributed to nest building and behaved similarly, with females and males present in the nest box for a comparable duration and transporting material to the nest equally often. However, while females spent more time constructing the nest, males tended to invest more time in vigilance, potentially as a means of coping with competition for nest cavities. These findings suggest a moderate degree of division of labour, which may facilitate cooperation. Moreover, some aspects of behaviour were related to proxies of reproductive success (lay date and egg volume). Females that contributed relatively more to bringing material laid earlier clutches and pairs that spent less time together in the nest box had larger eggs. Thus, selection pressures may act on how nest building pairs spend their time and cooperatively divide the labour. We conclude that cooperative nest building in birds could be associated with monogamy and obligate biparental care, and provides a vital but relatively untapped context through which to study the evolution of cooperation.

中文翻译：

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野生寒鸦对合作筑巢

动物使用其环境中的材料，可以单独或协作地创建各种结构。一个突出的例子是为繁殖而筑巢的鸟巢，它们可以保护后代免受外界压力（例如掠食者和温度）的影响，从而促进繁殖成功。为了成功地筑巢，鸟类需要做出各种决定，例如，关于巢的材料及其时间预算。迄今为止，研究主要集中于一种性别，而这种性别主要负责筑巢。相反，对两性构成巢穴的一夫一妻制物种的合作策略知之甚少。在这里，我们调查了两性在筑巢中的作用以及野生，一夫一妻制寒鸦对（Corvus monedula）行为的适应性相关性。我们表明，两个伙伴都对筑巢做出了贡献，并表现出相似的行为，雌鸟和雄鸟在巢箱中的停留时间相当，并且同样频繁地将材料运送到巢中。但是，尽管雌性花更多的时间建造巢穴，但雄性倾向于花更多的时间保持警惕，这可能是应对巢穴竞争的一种手段。这些发现表明中等程度的劳动分工，可能会促进合作。此外，行为的某些方面与生殖成功的代理有关（产蛋日期和卵量）。雌性对带出较早抓紧的材料做出了较大贡献，而在巢箱中在一起的时间较少的雌性卵较大。从而，选择压力可能会影响成对的筑巢工如何度过他们的时间并共同分工。我们得出的结论是，在鸟类中建立合作鸟巢可能与一夫一妻制和义务的双亲照顾有关，并为研究合作的演变提供了重要但相对尚未开发的背景。