I had shot some footage of a male Spruce Grouse and decided to see what Bent said about it. He reported a ca.1890 account by a Nova Scotia scientist and photographer named Watson L. Bishop. Here is what Mr. Bishop said:
"The red comb over each eye is enlarged until the two nearly meet over the top of the head...While he is strutting, the expanded tail is moved from side to side. The two center feathers do not move but each side expands and contracts alternately with each step as the bird walks...This attitude gives him a very dignified and even conceited air."
You won't find a description like that in Sibley! Anyway, here's the bird, slowed down 50%.
For higher definition: http://vimeo.com/25432997