How much Eurasian beaver activity is there in Italy? Using field signs to monitor and map a returned species

After centuries of widespread extinction, the Eurasian beaver Castor fiber has recolonised most of its former extent of occurrence, following international and national protection laws, reintroduction programmes, and unauthorized releases. Beavers provide valuable ecosystem services and multiple benefits to native biodiversity, though their activity may trigger conflicts with humans, especially in highly modified landscapes. Therefore, it is important to monitor their range-expansion, particularly at the early stages of the colonization process. This study quantifies beaver presence in Central and Northern Italy, where reproduction was first detected in recent years after five centuries of absence. A mix of techniques including both direct and indirect signs of presence was adopted to assess the occurrence and status of beavers in the area, retrieving data for the application of density estimators and, thus, population estimates. We document that at least 16 reproductive events occurred between 2021 and early 2023, with at least 55 areas of activity, located across three rivers of Central Italy, corresponding to a minimum of 40 individuals. Seven to ten individuals (in at least 5 areas of activity) were also recorded in Northern regions, in continuity with the populations occurring in neighboring countries beyond the Alps. Given the fast range expansion by the species and the potential for conflict with human activities, alongside the efficiency and applicability of our approach, this type of beaver field survey should be adopted by wildlife managers and policy makers both in areas of established presence but also in potential expansion areas, to develop management plans and to figure out opportunities this returning native species may bring.