Abstract
Rewilding has become a new paradigm to promote the natural recovery of many flagship species, including large carnivores. A better understanding of the factors that drive rewilding processes would allow predicting these in order to support them where desirable. Yet large-scale assessments of the factors that favor or limit mammal populations of conservation concern remain rare in Europe. This study sought to monitor changes in Eurasian otter (Lutra lutra) occupation over the years to identify the factors limiting its recolonization. To this end, we monitored otter signs and spraints over 1238 sampling sites in southwest France from 2003 to 2005 and then over 615 sites in 2011-2012. We modeled this dataset in a multi-season occupancy framework using biotic and abiotic covariates identified as potentially affecting otter detection, distribution and/or colonization rates. As otters are a cryptic and mobile mammal, we integrated detection probability and spatial autocorrelation (contagion) into the modeling design. Otter occurrence was detected at 31 % of the sites surveyed in 2003-2005 and 37 % of the sites surveyed in 2011-2012. Occupancy and colonization probabilities were strongly negatively correlated to the proportion of cultivated areas. Contagion covariates interacted strongly with other variables. These results suggest that, despite its recent colonization, the otter population in southwest France is still constrained in its expansion, notably by intensive agriculture. Natura 2000 schemes should incorporate rewilding approaches to further potentiate the colonization of this flagship species. Actions should focus on the conservation of natural riparian habitats and promote organic agriculture.