Breeding habitat preferences and niche partitioning of insectivorous songbirds in Alpine grasslands

Abstract

Alpine grasslands are increasingly facing pressures of climate and land-use changes. Higher temperatures and pastoral abandonment lead to treeline shift and to bush encroachment, while agricultural intensification causes soil eutrophication and landscape homogenization. Alpine grasslands in Europe host important populations of mountain specialists that are subject to range contraction, such as Water Pipits Anthus spinoletta. Moreover, insectivorous, ground-breeding migratory species, such as Northern Wheatears Oenanthe oenanthe and Whinchats Saxicola rubetra, still have stronghold populations in high-elevation habitats. These species are undergoing Europe-wide declines, and the Alps are a key region for their conservation. While lowland farmland has suffered acute biodiversity loss and received substantial research attention, fewer studies have characterized community composition and species-specific habitat preferences in changing Alpine grasslands. We conducted repeated bird surveys during the breeding season in a high-elevation valley. We analysed landscape-scale habitat use and fine-scale niche partitioning in the four most common insectivorous species, relating them to topography, vegetation productivity and habitat composition. Water Pipits, Northern Wheatears and Whinchats were most abundant in gently sloping, productive areas that are the prime target of pastoralism in mountain regions but are often subject to intensification. Shrub cover had positive effects on the abundance of Whinchats but was avoided by Water Pipits. Black Redstarts Phoenicurus ochruros had higher densities on steeper slopes. At a finer scale, species' niches partially overlapped, with clearer differentiation between Northern Wheatears, Whinchats and Black Redstarts. These divergent species-specific preferences call for maintaining landscape heterogeneity and low-intensity management, to preserve the crucial role of Alpine grasslands for declining species like Whinchats.