Antonio Antonucci, Giovanni Barbon, Eleonora Bianchi, Roberto Binatti, Romolo Caniglia, Paolo Ciucci, Antonio Di Croce, Giovanna Di Domenico, Luciano Di Martino, Graziana Dizonno, Alberto Dominici, Stefano Donfrancesco, Eugenio Duprè, Elena Fabbri, Daniele Falcinelli, Carmelo Gentile, Daniela Gentile, Patrizia Giangregorio, Elisa Laparra, Roberta Latini, Luigi Maiorano, Sara Marini, Federica Mattucci, Paola Morini, Nadia Mucci, Anna Padula, Davide Pagliaroli, Emanuela Peria, Fausto Quattrociocchi, Simone Ricci, Vincenzo Ruma, Valeria Salvatori, Luciano Sammarone, Giorgio Valle, Piero Genovesi.

Monitoring population size and spatial distribution of the critically endangered Apennine brown bear (Ursus arctos marsicanus) is paramount to inform and evaluate the efforts produced for its long-term conservation. In 2025, a comprehensive, non-invasive genetic sampling campaign was conducted across the subspecies' entire range in Central Apennines (Italy) to update abundance and distribution parameter estimates eleven years after the last systematic survey. We analysed multi-source genetic data (from rub trees, hair-snags, buckthorn aggregations and opportunistic sampling) using Spatial Capture-Recapture (SCR) models. SCR allowed to evaluate density variation across space and to explore its correlates.
Total population was estimated at 81 individuals (43 females, 38 males; 95% CI: 73–88). In the historical core area, the population remained stable and possibly close to saturation, slightly increasing from 51 bears (95% CI: 44–63) in 2014 to 56 bears (95% CI: 49–63) in 2025 (~4.4 bears/100 km²). When considering the newly expanded core area, the estimated population totals 65 individuals, while peripheral zones host 16 bears (95% CI: 9-22) at a tenfold lower density (0.4 bears/100 km²), showing a slight male bias (56%).
Crucially, the model showed that peripheral expansion is not limited by a lack of suitable habitat. Instead, range expansion is strongly governed by ecological connectivity and by the occurrence of anthropogenic mortality events. Peripheral zones well-connected via ecological corridors showed significantly higher bear densities, whereas areas lacking connectivity or highly exposed to human-induced mortality risks exhibited significantly reduced densities. Therefore, peripheral colonization remains fragile.
Future conservation priorities must focus on protecting and enhancing ecological corridors and on mitigating human-caused mortality (e.g., traffic collisions, poaching, poisoning, drowning in artificial basins, etc.), as these factors actively slow down or threaten to negate the establishment of new population nuclei in suitable territories.

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