Avalanche Tracks are Key Habitats for the Rock Bunting Emberiza cia in the Alps

In mountains, habitat mosaics, such as those found at the upper limit of coniferous forests in temperate regions, host relatively high avian diversity. In European mountains in particular, open-habitat bird species are threatened by a decrease in agro-pastoral activities and by global warming. Snow avalanches act as a natural agent of disturbance that maintains open habitats and thus may contribute to habitat heterogeneity at elevations below the treeline. Using the Rock Bunting Emberiza cia as a study species, we assessed the suitability of avalanche tracks as refuges for ecotone and semi-open habitat bird species. We studied habitat associations and other environmental factors that affect the species' occurrence based on data from point counts and habitat surveys carried out in the Alps. Rock Bunting presence was greater on avalanche tracks than in adjacent habitats at lower elevations. habitats with high Rock Bunting presence were characterised by a shrubby mosaic that was more open than the surrounding forest. There was no difference between avalanche tracks and control points at the treeline. Rock Bunting densities at avalanche tracks in the forest were similar to those in the treeline and the alpine belt, thus showing that avalanches create an ecotone habitat equivalent to the treeline at lower elevations. Rock Buntings used grassy habitats that had an intermediate rock cover, with patches of shrubs inside gullies. This optimal habitat probably provides nest sites that minimise exposure to predators whilst being close to patches of grass that provide foraging habitat. In a context of climate change, where avalanche activity might increase due to later snowfalls in spring, habitat mosaics created by this type of disturbance could play a fundamental role in the conservation of semi-open habitat bird species in the Alps.