Annual Grouse brood recruitment varies area by area - year over year. If you have a lot of song dogs, foxes and other predators, they'll hurt the population too. Predator prey cycle and all that.

To add, most Grouse hunters in WA hunt from the road. Get down into mixed habitat creek bottoms away from roads and you'll see more thunder chickens. One last tidbit...don't shoot at the first Grouse you see on a road or in an open area. They tend to send the dumb ones out first and if you can sit tight for a moment, the others will come out to play too.

Good luck,