Onset of autumn shapes the timing of birth in Pyrenean chamois more than onset of spring

1. In seasonal environments, birth dates are a central component for a species’ life history, with potential long-term fitness consequences. Yet our understanding of selective pressures of environmental changes on birth dates is limited in wild mammals due to the difficulty of data collection. In a context of rapid climate change, the question of a possible mismatch between plant phenology and birth phenology also remains unanswered for most species. 2. We assessed whether and how the timing of birth in a mountain mammal (isard, Rupicapra pyrenaica) tracked changes in plant growing season, accounting for maternal traits, individual heterogeneity, and population density. We not only focused on spring conditions but also assessed to what extent onset of autumn can be a driver of phenological biological events and compared the magnitude of the response to the magnitude of the environmental changes. We relied on a 22-year study based on intensively monitored marked individuals of known age....