Bears with a homey touch

To make progress on the road to repopulation, brown bears in the Pyrenees have learned not to cross paths with man, even if it means limiting their distribution and restricting their habitat. To what extent do human infrastructures, particularly roads, influence their use of space?

In 2004, Cannelle, the last female bear in the Pyrenees, was shot by a hunter whose path she had just crossed. She left behind Cannellito, an eight-month-old cub, the last descendant of the Pyrenean strain of this species. Today, Cannellito shares these steep forests with at least 76 other bears, most of them reintroduced from Slovenia, and 5 litters have been detected this year.

Under the radar

To monitor this population as closely as possible, the French Biodiversity Office (OFB), in collaboration with its Spanish and Andorran counterparts, relies on non-invasive methods such as photographic traps and hair traps, which are collected every month by the 450 volunteers in the Brown Bear Network. The Pyrenean bear population 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 real population", explains Maëlis Kervellec, modeller and doctoral student at the Centre d'écologie fonctionnelle et évolutive (Cefe) in collaboration with the OFB.

Under the supervision of Cefe researcher Olivier Gimenez, her thesis proposed the creation of density maps to facilitate their census. Using spatialized capture-recapture (SCR) models and location data from photographic traps and hair sampling, the young researcher has modeled bear distribution 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 possible barriers into account."

Away from the roads

Reintroduced in Ariège, bears have spread very little over the rest of the Pyrenees, despite the increase in their population. To what extent is their distribution limited by that of man? To answer this question, the doctoral student looked at 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 zones or patches of resources", explains Maëlis Kervellec, who used "all possible roads in her model, without distinguishing between large and small".

Unsurprisingly, the young researcher found that the greater the density of roads, the less likely bears were to use the habitat. She also observes that the Garonne valley between Vielha and Bagnère-de-Luchon seems to restrict the distribution of this Ariège core. " We can't say that the road is responsible for the bears restricting themselves to the area currently in use, because in this valley there are also other possible factors, such as the railroad or the river, which are not taken into account in my model," concludes Maëlis Kervellec. Further studies will undoubtedly enable us to better explain the behavior of this species, which remains critically endangered to this day.