The male Spruce Grouse can be distinguished from the Blue Grouse by always having white spotting or barring on the underparts. Blue Grouse is entirely dark below. The brown tip to the tail of most Spruce Grouse is different from the gray or black tip of the Blue Grouse. The "Franklin's" variety of the Spruce Grouse lacks the brown tip to the tail but has white spotting on the uppertail coverts that the Blue Grouse lacks. Female Spruce Grouse are very similar to female Blue Grouse but have black and white barring on the belly. Also, the terminal band on the tail is brown, not gray as in the Blue Grouse. Ruffed Grouse is browner and paler on the belly with a black subterminal band on the tail.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.