May brood desertion be ruled by partner parenting capability in a polygamous songbird? An experimental study

Abstract

Abstract Parents confront multiple aspects of offspring demands and need to coordinate different parental care tasks. Biparental care is considered to evolve under circumstances where one parent is not competent for all tasks and cannot efficiently raise offspring. However, this hypothesis is difficult to test, as uniparental and biparental care rarely coexist. Chinese penduline tits (Remiz consobrinus) provide such a system where both parental care types occur. Here, we experimentally investigated whether parents in biparental nests is less capable of caring than parents in uniparental nests. We monitored parenting efforts at (1) naturally uniparental and biparental nests and (2) biparental nests before and during the temporary removal of a parent. We found that total feeding frequency and brooding duration were similar for natural uniparental and biparental nests. Feeding frequency, but not brooding duration, contributed significantly to nestling mass. In line with this, parental removal revealed that the remaining parents at biparental nests fully compensated for the partner’s feeding absence but not for brooding duration. This reflects that the manipulated parents are confronted with a trade-off between feeding and brooding and were selected to invest in the more influential one. However, such a trade-off was not observed in parents of natural uniparental care nests. The different capabilities of a parent independently coordinating feeding and brooding tasks indicated that parents from biparental and uniparental nests experienced different environmental conditions.