[LUM#21] Bears who are a bit homebodies
To advance on the path to repopulation, brown bears in the Pyrenees have learned to avoid crossing paths with humans, even if it means limiting their distribution and restricting their habitat. To what extent do human infrastructure, particularly roads, influence their use of space?
In 2004, Cannelle, the last female bear in the Pyrenees, was shot by a hunter she had just crossed paths with. She left behind Cannellito, an eight-month-old cub, the last descendant of the Pyrenean strain of this species. Today, Cannellito shares these rugged forests with at least 76 other bears, most of which were reintroduced from Slovenia, and five litters have been detected this year.
Under the radar
To monitor this population as closely as possible, the French Biodiversity Agency (OFB), in collaboration with its Spanish and Andorran counterparts, uses non-invasive methods such as camera traps and hair traps, which are checked every month by the 450 volunteers of the Brown Bear Network. The bear population in the Pyrenees is now well known to observers, "but the more bears there are, the greater the risk that some of them will slip under the radar. As the monitoring effort is already very significant, we need to use statistical models to estimate the actual population," explains Maëlis Kervellec, modeler and doctoral student at the Center for Functional and Evolutionary Ecology (Cefe) in collaboration with the OFB.
Under the supervision of Olivier Gimenez, a researcher at Cefe, her thesis proposes establishing density maps to facilitate their census. Using spatialized capture-recapture (SCR) models and location data from camera traps and hair samples, the young researcher has modeled the distribution of bears on a larger scale. "Starting from the different locations where the animal has been detected, we try to represent how this individual uses the landscape in reality. By combining the space used by each bear, we obtain a distribution map that takes into account possible barriers."
Off the beaten track
Reintroduced in Ariège, bears have not spread widely across the rest of the Pyrenees mountain range, despite an increase in their population. To what extent is their distribution limited by that of humans? To answer this question, the doctoral student examined the impact of road infrastructure on landscape connectivity. "The term connectivity is defined here as the degree to which the landscape facilitates or hinders the movement of individuals between areas or 'patches' of resources," explains Maëlis Kervellec, who, in order to carry out this study, used "all possible roads without distinguishing between large and small ones" in her model .
Unsurprisingly, the young researcher found that the greater the density of roads, the less bears tend to use the habitat. She also observed that the Garonne valley between Vielha and Bagnère-de-Luchon seems to restrict the distribution of this Ariège core population. "We cannot say that the road is responsible for the fact that bears are restricted to the area they currently use, because in this valley there are also other possible factors, such as the railway line and the river, which are not taken into account in my model," concludes Maëlis Kervellec. Further studies will undoubtedly provide a better explanation of the behavior of this species, which remains critically endangered today.
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