Fitness consequences of male parental care in Savannah sparrows

Abstract

The fitness consequences of male parental care are central to life-history models of reproductive effort and the evolution of social and genetic mating systems. However, in a 4-year study (1992-1995) of Savannah sparrows (Passerculus sandwichensis) nesting on Kent Island, New Brunswick, Canada, male parental care during the nestling stage was only weakly related to offspring quality and survivorship. Females compensated for poor paternal performance by elevating their feeding rates, and they thus ameliorated selection on male parental care. The likelihood and size of subsequent broods was also unrelated to male feeding effort, suggesting the absence of some indirect (or 'female-mediated') benefits. These results were confirmed by an experiment in which male removal resulted in increased female feeding rates but had little effect on the number or quality of young. In contrast, previous research with multilocus DNA fingerprinting revealed a strong, positive relationship between a male's parental effort and his subsequent fertilization success. Together, this research suggests that the proximate and ultimate targets of male feeding effort can be distinct; traditional assumptions regarding the function of male parental care in birds may therefore be incomplete.