Size and spacing of grouse leks: comparing capercaillie (Tetrao urogallus) and black grouse (Tetrao tetrix) in two contrasting Eurasian boreal forest landscapes

Capercaillie (Tetrao urogallus L., 1758) and black grouse (Tetrao tetrix L., 1758 (= Lyrurus tetrix (L., 1758))) are two sympatric Eurasian lekking grouse species that differ markedly in habitat affinities and social organization. We examined how size and spacing of leks in pristine (Russia) and managed (Norway) forests were related to habitat and social behavior. Leks of both species were larger and spaced farther apart in the pristine landscape. Capercaillie leks were regularly spaced at 2-3 km distance, increasing with lek size, which in turn was positively related to the amount of middle-aged and older forests in the surrounding area. Black grouse leks were irregularly distributed at shorter distances of 1-2 km, with lek size explained by the size of the open bog arena and the amount of open habitat in the surroundings. At the landscape scale, spatial distribution of open bogs and social attraction among male black grouse caused leks to be more aggregated, whereas mutual avoidance in male capercaillie caused leks to be spaced out. In the pristine landscape, large-scale and long-term changes in forest dynamics owing to wildfires, combined with an aggregated pattern of huge bog complexes, presumably provide both grouse species with enough time and space to build up bigger lek populations than in the managed landscape.