Recolonization pattern of wolves in Northern Apennines, Central Italy: a Bayesian analysis using opportunistic and systematic data

Wolves (Canis lupus Linnaeus, 1758) have recolonized much of Europe and recently returned to the Apuan Alps (Central Italy), a partially isolated mountain chain unoccupied by wolves between 1850s and 2000s, after extirpation in early 1800s. Early stages of large carnivore recolonization often go undetected, particularly when standardized surveys are lacking. In the Apuan Alps, this left the spatiotemporal dynamics of wolf return unresolved. To reconstruct this process, we combined opportunistic playback-howling surveys (2007–2020) with camera-trap records (2011–2020), and fit a Bayesian occupancy model accounting for preferential sampling on camera-trap data. Playback surveys first confirmed reproduction in 2014; breeding units increased to four by 2018. Camera-trap occupancy rose 15-fold (2011–2018), despite early site-selection bias. Systematic sampling (2019–2020) validated these trends, estimating occupancy at ∼0.60 and detection probabilities threefold higher than opportunistic surveys. Opportunistic data could not fully detail early recolonization and spatial mechanisms due to likely misdetection of initial reproduction. Nonetheless, combined evidence suggested a two-phase pattern consistent with other wolf recolonizations: an initial lag period followed by rapid expansion via short-distance diffusion and jump-dispersal. Although prone to biases, opportunistic records can yield insights into cryptic recolonizations, guide early management and conservation, and inform future monitoring of recolonizing large carnivores.