Validating habitat suitability models for pine marten ( <i>Martes martes</i> ) reintroductions to England and Wales

Abstract Habitat suitability models (HSMs) are used extensively in conservation research and practice, particularly in reintroduction projects to identify prospective locations for translocations to take place. However, HSMs are only useful if their predictive capabilities are accurate; otherwise, there is a risk of reintroduction failures and misdirecting conservation actions. We validate and refine a HSM for pine marten ( Martes martes ) in Britain using an independent dataset of new observational data from two reintroduction projects and natural re‐colonisation. We test whether additional data on roads and trees outside of woodland improves the HSM predictions of habitat suitability and present an updated final HSM integrating all the observation data. We find the existing HSM adequately predicts pine marten presences but has random fit when considering both presences and absences. This is likely due to biases in the absence dataset which solely derives from failed scat transects on forest roads. The HSM reveals woodland cover at the 3 km scale is the key environmental factor for pine marten habitat suitability. The addition of data on roads and trees outside of woodland did not improve the fit of the HSM to the independent dataset. The updated model we present is therefore based on the original environmental inputs but uses up‐to‐date pine marten presences. Synthesis and applications: We present a validated HSM for pine martens in Britain which can be used to identify areas for future reintroduction projects, such as Devon and Cumbria, as well as areas where woodland planting could be targeted to improve habitat suitability and connectivity. Our adaptive methodology, which uses the monitoring data from reintroduction projects to validate and refine the HSMs created in the feasibility stage, can be applied to other species as reintroduction projects continue to grow in popularity. This ensures a robust basis for ongoing reintroduction suitability mapping and population recovery.