I did't know they drum in the winter. Kewl!
I hunted some thick reprod one winter about five years ago that was loaded with grouse and they were all in a drumming rampage. there had to be five at the very least, maybe as many as a dozen or more in there. as soon as one would stop another would answer. THudiddididdiddddddddd THudididididdddddddd thudiddddddddddddd- and it all went on for a good 20 minutes. if I didn't know what a grouse drum sounded like I would of thought that I was having some kind of heart or inner ear problem.
seems like the only reason I buy turkey tag anymore is to scout grouse spots and listen to drumming.