Lyrurus tetrix
Male differs from Capercaillie in smaller size, stockier build, curled outer tail-feathers and pure white under tail-coverts. Both sexes with white wing bars. Female more evenly speckled than Capercaillie, lacking brick coloured patches on breast an neck. Much less noisy when flushed than Capercaillie.
Song: a far reaching, continuous, bubbly cooing, occasionally interrupted by a hissing "chooo-eee". Female calls with a nasal "go-go-go-gooo", ending on a falling drawn-out note.
Wikipedia: map (se also Xeno-canto below)
Birdlife ecology