Life‐history theory predicts that parents refer to the resources they hold to determine their breeding strategy. In multi‐brooded species, it is hypothesized that single‐brooded parents produce larger clutches and raise offspring with a brood survival strategy, whereas multi‐brooded parents only do this under good breeding conditions. Under poor conditions, they produce smaller clutches and raise offspring with a brood reduction strategy. We tested this hypothesis in the Brown‐cheeked Laughing Thrush Trochalopteron henrici, which can breed twice a year on the Tibetan Plateau, by investigating the life‐history traits and provisioning behaviours of single‐ and double‐brooded parents. Single‐brooded parents laid larger clutches of smaller eggs and produced more and larger fledglings than double‐brooded parents in their first brood. Double‐brooded parents produced smaller clutches of larger eggs but fledged larger nestlings in their first brood than in their second brood. As single‐brooded parents only need to raise one brood a year, then producing and raising as many offspring as possible (i.e. the brood survival strategy in a large brood) can maximize their reproductive success. For double‐brooded parents, producing and raising fewer offspring in the first brood (i.e. the brood survival strategy in a small brood) can ensure their nesting success during a short breeding cycle. Additionally, producing more offspring but raising larger nestlings in the second brood (i.e. the brood reduction strategy in a large brood) can select for offspring of higher quality within the brood. Our findings indicate that different tradeoffs between single‐ and double‐brooded parents in egg‐laying and nestling‐raising may be an adaptation to the seasonal variation in environmental conditions.

中文翻译：

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父母在产前和产后阶段的数量和大小之间的权衡取舍的个体差异

生命史理论预测，父母会参考他们拥有的资源来决定其育种策略。假设在多亲动物中，单亲父母会产生更大的离合器，并通过亲子生存策略来繁殖后代，而多亲父母只有在良好的繁殖条件下才能这样做。在恶劣的条件下，它们会产生较小的离合器，并采用育雏策略来繁殖后代。我们在棕颊笑Th Trochalopteron henrici中检验了该假设通过调查单亲和双亲父母的生活史特征和供给行为，它每年可以在青藏高原繁殖两次。单亲的父母在他们的第一窝中比双亲的父母产下更大的卵较小的卵，并产生越来越多的雏鸟。双亲父母产生的卵较小，卵较大，但在第一个育雏中比第二个育雏出雏。由于单亲父母每年只需要繁殖一个育雏，然后繁殖并繁殖尽可能多的后代（即大育雏中的育雏生存策略）可以最大程度地繁殖。对于双亲的父母，在第一个亲代中产生并减少后代的数量（即 （在小型繁殖箱中繁殖）可以确保它们在短繁殖周期内成功筑巢。另外，繁殖更多的后代，但在第二个育雏中繁殖更大的雏鸟（即大型育雏中的减少育雏策略），可以选择育成更高品质的后代。我们的研究结果表明，单亲和双亲父母在产蛋和雏鸟育种方面的权衡取舍可能是对环境条件季节性变化的适应。