Extra-pair paternity and sexual selection in the Steller’s jay (Cyanocitta stelleri)

Genetic analysis of avian mating systems has revealed that more than 70% of monogamous species show incidence of offspring paternities that do not match the social father. Extra-pair paternity (EPP) has been linked to a variety of factors, including size and symmetry of ornamental traits, coloration, resource availability, and local conspecific density. I examined how ornamental plumage traits of individual Steller's jays (Cyanocitta stelleri) and territory characteristics influence genetic fidelity of socially monogamous pairs, in an area of high population density. I used seven highly polymorphic microsatellite markers to assign paternity to 79 offspring, and identified 12 (15.2%) as extra-pair young. Steller's jays with extra-pair young had significantly lower values of feather brightness and hue, indicating more ultraviolet-blue shifted coloration, and nested in closer proximity to the forest edge than Steller's jays with no detected extra-pair young. Body size, crest height, asymmetry of ornamental crest stripes, as well as vegetative composition of territories and their proximity to supplemental feeders appeared to have little relationship to EPP. These results indicate that extra-pair paternity plays a role in the mutual selection of secondary sexual characteristics, and suggest local density, and perhaps availability of resources such as anthropogenic food, may influence Steller's jay mating dynamics.