Direct benefits of mate choice: a meta-analysis of plumage colour and offspring feeding rates in birds.

Mate choice is generally costly to the choosy sex, so fitness benefits must counterbalance these costs. Genetic benefits of choice are widely examined and have received overall support. Direct benefits such as high quality parental care by highly ornamented individuals are widely assumed to be important but are less frequently tested, theoretically debated, and their support in the recent literature is unknown. Furthermore, in taxa where both sexes provide care, the preferential investment of the partner in relation to ornamentation may reduce own investment and modify apparent parental care quality. In a phylogenetically controlled meta-analysis, we collated correlative results from birds concerning parental plumage coloration and the nestling feeding rates of the ornament bearer and its partner. Overall evidence was weak for signalling of parental care quality and somewhat stronger for preferential partner investment. Surprisingly, the sex of the signaller and the type of plumage colour seemed to exert weak effects on the signalling of parental care quality. Finally, there was a group of cases with opposite relationships of care and ornamentation in the two parties. We found that this group arose predominately from preferential partner investment in relation to ornamentation, with concomitant, but weaker, reduction of own investment. We conclude that the effect of partner investment on parental care indication seems system-specific and needs further study.