Description: We calculated the habitat suitability raster map for territorial males (spatial resolution 100 100 m) using the model-building tool in ArcMap (ver. 9.2). Before the calculation we developed a land filter (total 8148 km2), based on Pedersen et al. (2007), consisting of land areas below 600 m (anticipated to be potential ptarmigan habitat) without glaciers and moraines (a buffer of 1 km was set around moraine areas). The map describes habitat suitability on a scale from 0 (not suitable) to 1 (highly suitable) and for visualization we categorized habitat suitability into four classes (marginal 0–0.099, low 0.10–0.399, medium 0.40–0.699, high 0.70–1.00). The flat valley bottoms and mountain plateaus ( 600 m) were natural borders between the lowest habitat suitability classes (classes marginal and low), and the remaining values from 0.1–1.0 were divided into three
habitat suitability classes.