Achromatic plumage reflectance predicts reproductive success in male black-capped chickadees

The size of achromatic (black, white, gray) plumage patches serves as a male status signal in many species of birds, but variation in the colors of these patches has received little attention. We assessed the relation between achromatic plumage reflectance, dominance rank, body condition, and reproductive success in male black-capped chickadees, Poecile atricapillus. We measured plumage reflectance for five body regions of 40 male chickadees in late winter and monitored these males throughout the following breeding season to determine whether they survived to breed, whether they successfully paired, whether their partner laid eggs, and both their apparent and realized reproductive success. As expected from past studies, a male's dominance rank significantly predicted whether his partner laid eggs. However, only achromatic plumage reflectance significantly predicted other measures of male reproductive performance. Among males who fledged at least one offspring, both the brightness of white plumage regions and the UV-chroma of melanin-based plumage regions were significant predictors of the proportion of within-pair young in their nests. When we consider all males we measured, assigning zero values to males who failed to sire any offspring, the UV-chroma of melanin-based plumage regions was a significant predictor of realized reproductive success. Bib size was also related to male realized reproductive success. Our findings suggest that individual variation in achromatic plumage may play an important role in sexual signaling in chickadees.