Environmental forcing, individual repeatability, and mother–daughter resemblance shape the phenology of a long-lived seabird

Climate change and variability push species to shift their distributions and phenology to track their climatic niche. Predicting population responses requires identifying the environmental cues that trigger reproduction, their fitness consequences, and the intrinsic factors that shape individual breeding decisions. In long-lived species with deferred breeding, extrinsic (environmental) and intrinsic (individual/maternal) factors may interact in shaping responses to environmental change, but direct empirical evidence remains scarce. We use 2065 breeding events collected over 22 y on a wide-ranging seabird, the Scopoli’s Shearwater. We quantify the effects on population mean laying date of a large-scale climatic index (wNAO) associated with oceanographic conditions. We assess how individual breeding experience and mother–daughter resemblance contribute to among-female differences in reproductive timing, and evaluate the consequences for breeding success (BS) and adult survival. Average laying date was earlier under negative phases of wNAO, indicating a plastic response at the population level. Individual repeatability in the relative laying date (RLD) was high ( R = 0.50) irrespective of experience, indicating consistency among females. Using 142 mother–daughter cases, daughters’ RLD resembled those of their mothers, a covariance that may reflect genetic inheritance, maternal effects, or shared environment. Early laying was associated with higher BS and survival, translating into an annual fitness advantage. Differences in survival and BS across individuals were more evident during the first observed breeding attempts. Together, these results support a scenario in which plasticity shifts the population mean breeding date in response to climatic variation, while persistent traits generate differential fitness among individuals.