Plumage color and food availability affect male reproductive success in a socially monogamous bird

Male reproductive success in socially monogamous birds is influenced to varying degrees by within-pair fertilization (WPF) and extrapair fertilization (EPF). In many species, males of higher phenotypic quality (e.g., plumage color) are more likely to obtain EPFs; however, predictors of WPF success have been less consistently identified. Moreover, few studies have examined the influence of ecological variables on patterns of paternity, even though environmental conditions are known to affect mating behavior of male and female birds. In this study, we examined phenotypic and ecological factors influencing patterns of paternity in broods of mountain bluebirds, Sialia currucoides. We show that brighter, bluer males were more likely to obtain EPFs in first broods but that plumage color did not predict the ability of males to maintain paternity in their own nest. We then examined the effect of food availability in first broods on the probability of males losing paternity in second broods within the same season. Females that were provided with supplemental food throughout first breeding attempts were less likely to produce extrapair offspring in second broods, and we suggest that supplemented females may have been less likely to seek extrapair mating opportunities because they perceived their social mates to be of higher quality under conditions of enhanced food availability. Our results demonstrate that ecological variables such as food availability can influence patterns of paternity and suggest that consideration of environmental context will be important for future research investigating mate choice and sexual selection in socially monogamous species. Copyright 2011, Oxford University Press.