Inequality among offspring, correlates of recruitment and lifetime reproductive success in a long-lived raptor

Early-life conditions may impact an individual’s ability to survive long enough to reach breeding age as well as its lifetime reproductive success (LRS). We examined how different aspects of parental quality and natal territory habitat were correlated with the probability of recruitment and subsequent LRS in a top avian predator. Using resight and banding data from a 30-year demographic study on Swainson’s Hawks (Buteo swainsoni), we first examined factors related to recruitment probability, followed by a secondary follow-up analysis we explored correlates of reproductive success, tracking the same individuals as they progress through major life stages. Our analysis tracks only individuals marked as nestlings and where both parents were also uniquely marked and known to the study. This marking requirement allowed us to examine mated pair characteristics while simultaneously separating the effects of parental experience by sex. Pair bond duration best explained recruitment and was positively correlated with the probability of offspring being recruited into the local breeding population. For individuals that survived the challenges of early life and recruited, a far smaller subset of individuals, we found that maternal experience best predicted an offspring’s quality, as expressed by LRS, receiving twice the support of other models. Surprisingly, while pair bond duration correlated with recruitment probability, it was not predictive of offspring LRS. These modeling steps mirror the progressive removal of frail individuals from the population, and reveal that different aspects predict success in advancing life stages. We hypothesize that more established pairs can successfully fledge lower quality offspring that recruit but subsequently have low lifetime reproductive success, while maternal effects have a large influence on offspring quality.