Integrating opportunistic and structured non-invasive surveys with spatial capture-recapture models to map connectivity of the Pyrenean brown bear population

Abstract

Connectivity is a key driver of the recovery and expansion of endangered populations and has to be evaluated in management plans. In practice, connectivity is difficult to quantify especially for rare and elusive species. Here, we use spatial capture-recapture (SCR) models with an ecological detection distance to identify barriers to movement. We focused on the transnational critically endangered Pyrenean brown bear (Ursus arctos) population, which is distributed over Spain, France and Andorra and is divided into two main cores areas following translocations. We integrate structured monitoring from camera traps and hair snags with opportunistic data gathered after depredation events. While structured monitoring focuses on areas of regular bear presence, the integration of opportunistic data allows us to obtain information in areas where the species is absent, which is especially important for ecological inference. By estimating a resistance parameter from encounter data, we show that the road network impedes movements. In areas with high road length (6.70 km/km2), the home range size of brown bears is reduced up to two-fold compared to areas with low road length (0.93 km/km2). Overall, the connectivity between the two cores areas is limited, as well as the expansion of the population to the west. When assessing connectivity, spatial capture-recapture modeling offers an alternative to the use of experts’ opinion when telemetry data are not available.