[LUM#21] Bears Who Are a Bit Homebodies
To make progress toward repopulation, the brown bears of the Pyrenees have learned to avoid crossing paths with humans, even if it means limiting their range 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 she had just encountered. She left behind Cannellito, an eight-month-old cub, the last surviving member of the Pyrenean population of this species. Today, Cannellito shares these rugged forests with at least 76 other bears, most of which are the result of the reintroduction of individuals brought from Slovenia, and five litters have been detected this year.
Under the radar
To monitor this population as closely as possible, the French Office for Biodiversity (OFB), in collaboration with its Spanish and Andorran counterparts, relies on non-invasive methods such as camera traps and hair traps, which are checked monthly 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. “Since the monitoring effort is already very extensive, we need to use statistical models to estimate the actual population,” explains Maëlis Kervellec, a 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 aims to create density maps to facilitate bear censuses. Using spatialized capture-recapture (SCR) models and location data from camera traps and hair samples, the young researcher has modeled bear distribution on a larger scale. “Starting from the various locations where the animal has been detected, we try to represent how this individual actually uses the landscape. By combining the areas used by each bear, we obtain a distribution map that accounts for potential barriers.”
Far from the roads
Although bears have been reintroduced in Ariège, they have not spread widely across the rest of the Pyrenees mountain range, despite the growth of their population. To what extent is their distribution limited by human activity? 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 impedes—the movement of individuals between areas or ‘patches’ of resources,” explains Maëlis Kervellec, who, to conduct this study, included “all possible roads in her model without distinguishing between major and minor ones.”
Unsurprisingly, the young researcher notes that the higher the road density, the less bears tend to use the habitat. She also observes that the Garonne Valley between Vielha and Bagnère-de-Luchon appears to limit the range of this Ariège population. “We cannot say for certain that the road is responsible for the bears being confined to their current range, because in this valley there are other possible factors, such as the railroad tracks or the river, that are not accounted for in my model,” concludes Maëlis Kervellec. Further studies will surely shed more light on the behavior of this species, which remains critically endangered today.
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