Crosses between male black grouse Tetrao tetrix and female capercaillie T. urogallus are the most common grouse hybrids. Some male hybrids (F₁-generation) may be fertile and produce offspring (F₂-generation) with females of capercaillie and, rarely, black grouse. Specimens and descriptions of lek behaviour are also available for probable F₃- and F_>3-hybrids. Three and two male F, hybrids were documented to display simultaneously on a black grouse lek in Norway (1993–1997), and solitarily displaying hybrids were documented on black grouse leks in the Czech Republic (1960–64), Sweden (1991–93) and Norway (1992). Mating of hybrid males with female capercaillie was observed in 1992 and 1994. The lekking behaviour of the hybrids and their attitudes towards other tetraonids are described.