Quantification of ecological preferences of the Capercaillie Tetrao urogallus by means of the habitat suitability index: a case study in the Augustow Forest (N-E Poland)

Habitat structure and selection by the Capercaillie Tetrao urogallus were assessed in the Augustow Forest (NE Poland), where a population of 50–80 birds and 11 active leks existed. Habitat preferences in the local scale were studied, based on measurements of total 1952 circular sample plots with radius of 15 m. On plots, in total, 10 variables describing forest structure (e.g. successional stage, canopy cover, vertical stand structure, share of Scots pine Pinus sylvestris, shrub layer cover, bilberry Vaccinium myrtillus cover, average height of ground vegetation, occurrence of feeding and roosting trees), as well as signs of Capercaillie presence, were assessed. Then, the model of Habitat Suitability Index (his) was constructed. Plots with high HSI scores were used by Capercaillie more often than expected in a case of a random choice, and those with low scores – less than expected. Capercaillie in the Augustow Forest prefers relatively old, one-layered stands, dominated by Scot pine with a sparsely developed shrub layer. The most important differences between abandoned and active leks were related to shrub cover in ground vegetation and height of ground vegetation and share of bilberry.