In socially monogamous species with bi-parental care, males may face a trade-off between providing parental care and pursuing extra-pair matings. The "parenting-mating trade-off" hypothesis predicts that high-quality males-who have greater potential to gain extra-pair matings, for example, larger males usually win the competition for extra-pair mating-should reduce parental care and spend more time looking for extra-pair matings. However, the trade-off between parenting and mating efforts may be complicated by variation in the availability of extra-pair mating opportunities. By using field data of hair-crested drongos (Dicrurus hottentottus), a species exhibiting bi-parental incubation behavior, collected in central China from 2010 to 2017, we tested whether the potential negative relationship between male quality and paternal care was dependent on the number of nearby fertile females. We found that male drongos mainly seek extra-pair matings during the incubation period and high-quality individuals (males with longer tarsi) are more likely to sire extra-pair offspring. In agreement with the "parenting-mating trade-off" hypothesis, high-quality males incubated less by recessing longer between incubation bouts. However, this was only the case when sufficient fertile females nearby for extra-pair mating opportunities. Females compensated for reduced male care, but this was independent of male quality. This suggests that the reduction in care by high-quality males might be a direct response to extra-pair mating opportunities rather than facilitated by differential allocation of females. Our results indicate that individual quality and available mating opportunities may shape the optimal trade-off between parental care and seeking additional matings for males. Lay Summary: How do individual quality and the number of potential extra-pair mates influence the optimal trade-off between parental care and engaging extra-pair courtship in animals? In hair-crested drongos, high-quality males, who are more successful in obtaining extra-pair fertilizations, reduced their share in incubation, but only when they had sufficient extra-pair mating opportunities. Females partially compensate for the reduced incubation of their partners, but the compensation was not affected by male quality.

中文翻译：

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一对额外的交配机会在鸣禽中调解育儿和交配努力的权衡

在具有双亲照顾的社会一夫一妻制物种中，雄性可能会面临提供父母照顾和追求额外配对之间的权衡。“育儿-交配权衡”假说预测，高品质的雄性——更有可能获得多对交配，例如，体型较大的雄性通常会赢得多对交配的竞争——应该减少父母的照顾并花费更多时间寻找额外的配对交配。然而，育儿和交配努力之间的权衡可能会因额外配对交配机会的可用性变化而变得复杂。利用2010-2017年在华中地区采集的具有双亲孵化行为的毛凤头龙（Dicrurus hottentottus）野外数据，我们测试了男性素质与父亲照顾之间的潜在负面关系是否取决于附近可育女性的数量。我们发现雄性 drongo 在潜伏期主要寻求额外的交配，并且高质量的个体（跗骨较长的雄性）更有可能产生额外的后代。与“育儿-交配权衡”假设一致，高质量的雄性通过在两次孵化之间的休息时间更长而孵化的更少。然而，只有当附近有足够多的可育雌性提供额外的交配机会时才会出现这种情况。女性补偿了男性护理的减少，但这与男性素质无关。这表明高质量雄性的照顾减少可能是对额外配对机会的直接反应，而不是雌性的差异分配所促成的。我们的结果表明，个体素质和可用的交配机会可能会在父母照顾和为雄性寻求额外交配之间形成最佳权衡。小结：个体素质和潜在的多对伴侣的数量如何影响父母照顾和在动物中进行多对求爱之间的最佳权衡？在毛冠龙哥中，在获得额外对受精方面更成功的高品质雄性减少了它们的孵化份额，但前提是它们有足够的额外配对交配机会。女性部分补偿了伴侣孵化的减少，