Reproductive decisions in American robins (Turdus migratorius): Relationships among paternity allocation, parental care, plumage variation, and mate choice

Considerable theoretical and empirical effort has been devoted to examining how individual ecological and evolutionary factors shape breeding decisions in birds, but we are only beginning to address how these factors can interact to shape behavioral outcomes, particularly in species with overlapping broods. In my dissertation, I addressed the reproductive consequences of behavioral interactions between males and females over multiple breeding attempts, specifically by examining how these interactions affect mate-guarding opportunity, extra-pair paternity (EPP), parental care, and mate choice in the American robin, Turdus migratorius, a socially monogamous, multi-brooded songbird. Reproductive success in American robins was strongly influenced by the number of nesting attempts made in a single breeding season and the likelihood of making multiple nesting attempts was associated with initial nesting success and the timing of breeding onset. EPP was common, but patterns of paternity were not associated with seasonal variation in breeding density or with variation in mate-guarding opportunity associated with overlapping broods. While EPP was associated with the length of time between broods, suggesting a potential relationship between parental care in early broods and paternity allocation in later broods (the quid pro quo hypothesis), the data failed to support this hypothesis. American robins appeared to mate assortatively based on two melanin-based plumage traits, breast plumage color and tail spot damage. These traits were associated with measures of individual quality and breeding performance, but differed in the information conveyed in each sex. Males with darker plumage color were in better condition and females with darker plumage and less tail spot damage fledged more young in better condition. However, plumage trait expression did not predict parental quality in either sex. Overall, the findings of my dissertation suggest that the behavioral outcomes associated with reproductive decisions in American robins are affected by interactions among individual quality, mate choice, paternity allocation, parental care, and sexually-selected plumage traits. The fact that other species of songbirds show ecological similarities with American robins suggests the potential for these interactions and the resulting reproductive strategies to apply more broadly.