Landscape characteristics influence regional dispersal in a high-elevation specialist migratory bird, the water pipit Anthus spinoletta.

Species living in high mountain areas are currently threatened by climate change and human land use changes. High-elevation birds frequently inhabit island-like suitable patches around mountain peaks, and in such conditions the capability to exchange individuals among patches is crucial to maintain gene flow. However, we lack information regarding the dispersal ability of most of these species and the possible influence of landscape features on dispersal. In this study, we used population genomics and landscape resistance modelling to investigate dispersal in a high-elevation specialist migratory bird, the water pipit Anthus spinoletta. We aimed to assess the levels of gene flow in this species within a wide area of the European Alps, and to assess the effects of environmental characteristics on gene flow, by testing the isolation by distance (IBD) hypothesis against the isolation by resistance (IBR) hypothesis. We found clear support for IBR, indicating that water pipits preferentially disperse across suitable breeding habitat (i.e., high-elevation grassland). IBR was stronger in the part of the study area with less extended suitable habitat. Landscape resistance was slightly better described by habitat suitability models than landscape connectivity models. Despite the observed IBR, gene flow within the study area was high, probably also because of the still wide and relatively continuous breeding range. The forecasted reduction of range of this species may lead to stronger effects of IBR on gene flow. Other high-elevation specialist birds may show similar IBR patterns, but with possibly stronger effects on gene flow because of their more reduced and patchy habitats.