Behavioural plasticity shapes population ageing patterns

Studying the mechanisms shaping age-related changes in behaviour ("behavioural ageing") is important for understanding population dynamics in our changing world. Yet, studies that capture within-individual behavioural changes in wild populations of long-lived animals are still scarce. Here, we used a 15-year GPS-tracking dataset of a social obligate scavenger, the griffon vulture (Gyps fulvus), to investigate age-related changes in movement and social behaviours, and disentangle the role of behavioural plasticity and selection in shaping such patterns. We tracked 142 individuals for up to 12 years and found a non-linear increase in site fidelity with age. This pattern resulted from individuals changing behaviour throughout their life (behavioural plasticity) and not from selective disappearance. Mature vultures increased the predictability of their movement routines and spent more time at prime roosting sites compared to younger individuals. Thus, adults likely have a competitive advantage over younger conspecifics. These changes in site fidelity and movement routines were mirrored in changes to social behaviour. Older individuals interacted less with their associates (decreasing average strength with age), particularly during the breeding season. Our results reveal a variety of behavioural ageing patterns in long-lived species and underscore the importance of behavioural plasticity in shaping such patterns. Comprehensive longitudinal studies are imperative for understanding how plasticity and selection shape the persistence of wild animal populations facing human-induced environmental changes.