Age-related movement behaviour as a window into population dynamics

Heterogeneity in individual performance drives changes in population size, resilience, and future trajectories, as differences in life-history tactics can shift sex ratio, age structure, and ultimately population growth. In many vertebrates, age structure is a fundamental driver of population dynamics, predicting variation in survival, recruitment, and breeding success. Yet a key gap remains: what mechanisms generate age-related differences in vital rates? Competing, and potentially complementary, explanations include improvement through experience and efficiency, selective disappearance of low-quality individuals, and late-life senescence. A plausible mechanistic link is foraging success and efficiency, because it directly influences breeding output and survival. However, age-dependent foraging strategies remain poorly understood in many vertebrates, including small pelagic seabirds. Using high-resolution GPS tracking of known-age European Storm-petrels (Hydrobates pelagicus) during incubation in the West Mediterranean, we test whether age-specific differences in vital rates are reflected in movement and behavioural tactics. By quantifying trip attributes and behavioural time budgets, and relating them to environmental context and individual heterogeneity, we aim to identify movement-derived mechanisms that can help explain age-related demographic variation and, ultimately, improve forecasts of population change.