Coordinated parental provisioning is related to feeding rate and reproductive success in a songbird

In species with biparental care, there is sexual conflict over parental investment because each parent benefits when their partner bears more of the reproductive costs. Such conflict can be costly for offspring, but recent theoretical work predicts that parents can resolve sexual conflict through behavioral negotiation, specifically by alternating their trips to provision nestlings. However, this idea has received almost no empirical attention. In this study, we test the hypothesis that parents alternate their delivery of food to offspring in long-tailed tits (Aegithalos caudatus) and investigate whether this coordination of parental care is associated with greater reproductive success. We show that parents alternate provisioning trips more than would be expected by chance and that parental alternation is repeatable across multiple observation periods at a nest. More alternation is associated with increased visit synchrony and increased food delivery to nestlings. Moreover, we found that nests with more alternation were less likely to be predated, probably resulting from reduced activity around the nest when parents coordinate their provisioning behavior. Our results support the hypothesis that alternation of offspring provisioning is a behavioral adaptation to reduce the costs of sexual conflict.