Age structure of Capercaillie males (Tetrao urogallus) in NW Russia may reflect two-way movements – a hypothesis

Abstract

Skulls of Capercaillie (Tetrao urogallus) males collected in NW Russia in 1980-2008 showed two different types of age structure. In native forest and bog-forest tracts with high Capercaillie density (-2.0 birds/km2 in spring) there were relatively more 2- and 3-year-old males and correspondingly fewer yearlings and youngsters. The converse applied over the vast adjacent logged areas where Capercaillie density was lower (~ 0.6 birds/km2), with fewer 2- and 3-year-old males and more yearlings and youngsters. The results were consistent with emigration of youngsters from native into logged areas and a reverse movement of maturing cocks attempting to join the big leks on native areas. The v evidence suggested that survival of cocks over 3 years old was low in both habitat types, perhaps due to continued emigration from logged areas plus mortality associated with competition for status at the big leks on native areas. Such movements presumably occur mostly at times of high population density.