Born to be Bold? Personality Traits and Reproductive Performance in Magellanic Penguins ( Spheniscus magellanicus )

ABSTRACT Personality differences in animals are defined as consistent behavioral variation among individuals and are known to influence fitness. However, the mechanisms by which personality traits affect fitness remain largely underexplored. In this study, we assessed intra‐annual boldness in Magellanic penguins ( Spheniscus magellanicus ) from a breeding colony on Isla Quiroga, Argentina, using a novel object test during incubation and chick‐rearing. We estimated its repeatability, examined whether boldness correlated with reproductive performance, and explored how this relationship varied across years with differing resource availability and environmental conditions. Boldness remained consistent over the breeding season, and we found a negative association between male boldness and reproductive success, as bolder males fledged fewer chicks. In addition, although boldness was not associated with mate choice, pairs with similar boldness exhibited intermediate reproductive success (approximately one fledgling from two eggs). Overall, our findings indicate that variation in boldness behavior may play a role in shaping reproductive success in this species.