Hazel & Black Grouse
A quick survey of recent treatments...
Tetrastes bonasia: Madge & McGowan 2002 (Pheasants etc), H&M3, Zoonomen, IOC, TiF, King 1997, Dutch Birding, OSME, OBC, China Bird Report.
Bonasa bonasia: de Juana 1994 (HBW 2), Monroe & Sibley 1993, BirdLife, Cornell...