Outdoor recreation causes effective habitat reduction in Capercaillie Tetrao urogallus: a major threat for geographically restricted populations

Outdoor recreation inflicts a wide array of impacts on individual animals, many of them reflected in the avoidance of disturbed areas. The scale and spatial extent, however, at which wildlife populations are affected, are mostly unclear. Particularly in geographically isolated populations, where restricted habitat availability may preclude a relocation to undisturbed areas, effective habitat reduction may remain underestimated or even unnoticed, when animals stay in disturbed areas and only show small-scale responses. Based on telemetry data of 12 individuals, we investigated the spatial and seasonal effects of outdoor recreation, on western capercaillie Tetrao urogallus, considering two scales, homerange and within-homerange habitat selection. We determined the distance-thresholds up to which recreation infrastructures were avoided and estimated the extent of affected habitat for the isolated Black Forest (Southwestern Germany) study population. While outdoor recreation did not affect homerange selection, strong effects on habitat use within the homerange were detected: Distance to recreation infrastructure (hiking and cross-country skiing trails, ski pistes) was the main determinant of habitat selection in winter; in summer, mountain bike trails and hiker's restaurants were avoided up to an average distance of 145m (CI: 60-1092m). Around winter-infrastructure, relative avoidance was recorded up to 320m (CI: 36-327m), it was reduced, however, when dense understory provided visual cover. Of the entire population area, between 8-20% (summer) and 8-40% (winter) were affected by outdoor recreation, mainly in the high altitudes. Even without evident large-scale shifts in species distribution, local-scale avoidance of outdoor recreation can substantially contribute to effective habitat reduction. Based on our results we recommend a general reduction in recreation infrastructure density in key habitats, the establishment of undisturbed wildlife refuges with a diameter of at least 800m, as well as enhancing visual protection by maintaining a strip of dense understory along trails.