Back to the river: Behavioural patterns of Eurasian beavers recolonising central Italy

Newly introduced species may alter the structure and functioning of colonised ecosystems, particularly when they act as ecosystem engineers. The Eurasian beaver Castor fiber, historically present in central Italy until the Middle Ages, has recently reappeared in the region. Despite growing evidence of its ecological impacts, detailed information on its behavioural repertoire in Mediterranean environments is lacking. Here, the first comprehensive behavioural assessment of Eurasian beavers recolonising central Italy using intensive camera trapping across three river systems is provided. From March 2023 to May 2024, 24 distinct behavioural patterns were recorded and their occurrence and duration were quantified across age classes, sex, and seasons. Behavioural expression was strongly age-dependent: juveniles showed significantly higher levels of play, allogrooming, nose-touching, and exploratory behaviour, while subadults exhibited increased diving and exploration, indicating a transition towards independence. Adults displayed a broader and more functional repertoire, with higher frequencies of swimming, vigilance, scent marking, and material transport on land, reflecting their role in territory maintenance and construction activities. Seasonality also shaped behaviour markedly. Dam-building and digging activities and swimming were significantly more frequent during the cold period, whereas self-grooming sharply increased during warm period, suggesting thermally-driven behavioural plasticity. Model comparisons revealed that social and developmental behaviours were best explained by age, whereas construction and maintenance behaviours were primarily driven by seasonal conditions. Compared with northern European populations, Italian beavers showed lower building frequencies but increased terrestrial and swimming activities, suggesting context-dependent behavioural adjustments shaped by local ecological conditions.