Knowledge of a species’ age-specific pattern of survival and reproduction is fundamental to understanding its life history evolution and population dynamics. We investigated the age-specificity of various traits in the Banter See common terns. We found that while survival probability monotonously declined with age (Zhang et al. 2015a), various phenological and reproductive traits gradually improved with age, before levelling off (Zhang et al. 2015b). These age-related improvements were mostly due to within-individual changes in trait expression, and while effects of selective appearance and disappearance provided evidence for quality differences between individuals, these effects were small (Zhang et al 2015b). Correcting for changes in trait expression with age, we found within-individual variation in phenology and reproductive success to be associated with mortality risk (Zhang et al. 2015c). Specifically, we found that if individual birds arrived and bred earlier than they did on average and laid larger clutches and eggs than they did on average, their mortality risk increased. We therefore showed that when quality differences between birds (Vedder & Bouwhuis 2018) are accounted for, survival costs of early and successful reproduction can be observed (also see Vedder et al. 2021). Finally, we combined performance measures to calculate age-specific reproductive values, and found evidence for senescence (Zhang et al. 2015a). The fitness cost of this senescence was, at ~20%, slightly higher than reported for other bird species (Bouwhuis & Vedder 2017).

Across generations, we found ageing parents to produce more male- than female-biased broods, as well as sex-specific pathways of parental age effects on offspring lifetime reproductive success: recruited sons from older fathers suffer from a reduced lifespan, while recruited daughters from older mothers suffer from reduced reproductive performance throughout life (Bouwhuis et al. 2015). The latter effect may (partly) be explained by daughters from older mothers fledging with a reduced body mass and remaining a low body mass throughout life (Bouwhuis et al. 2015), a pattern that itself cannot be explained by sex- and age-specific parental provisioning behaviour (Cansse et al. 2024).