• Ixodes ricinus, the most common tick in Central Europe, is an important vectorof pathogens threatening human and animal health.• Tick abundance and repartition increased during last decades with globalenvironmental changes in the continent, which include climate and habitatchanges, and increase of deer densities.• Indeed, cervid species are identified as key hosts to ticks, especiallyroe deer (Capreolus capreolus) whose populations have increased inrecent years in France and Europe.• Mammal newborns have a naïve and immature immune system and aretherefore more vulnerable to tick infestations.• Thus it is important to improve knowledge of factors influencing the tickburden of neonates. Here, we study roe deer fawns monitored during 27 yearsin a French population with a novel Bayesian model.