Hatching order explains an extrapair chick advantage in western bluebirds

摘要: Within-family comparisons of offspring growth rates have provided important tests genetic benefits extrapair mating for females. Here, we demonstrate that hatching order explains the advantage young in western bluebirds (Sialia mexicana); nestlings are larger than within-pair same nest, but they also hatch earlier clutch, thus benefiting from asynchrony. By controlling and other nongenetic factors comparing mixed-paternity broods with genetically monogamous broods, show nestling is not based. We cannot rule out possibility females benefit because quality indicators may appear later life be independent order, however, based on our results, do see evidence superiority nestlings. Although findings similar to ours been attributed maternal effects, it currently unclear whether overrepresentation early laying sequence results investment patterns females, their social mates, or males. This study highlights need investigate potentially complex interactions among all players, how these lead higher performance compared within family. Key words: paternity, benefits, asynchrony, effects. [Behav Ecol]