first off when you hear about grouse cycle's its referring to ruffed grouse ONLY (washington has three species of forest grouse) and I believe most of the information on the grouse cycle pertains to the midwest to the east coast. I am not sure if there has been much cycle research done for the western states, let alone western washington which I think should be the biggest anomaly out of all the states. the biologists I talked about western Wa grouse believe in a cycle but think wet springs effect them more.
some (east coast cycle devotees) theorize that the cycle has to do with canadian birds of prey migrating south when rabbits are in short supply to the north. they feed heavily on "southern" grouse for a number of years until the population declines and they move back up north to feed on fortified population rabbits once again, leaving the grouse population alone and let their numbers grow. another thought is the rabbits have a parasite that builds up in the birds of prey, killing them off creating less predators for the grouse as well as a rabbit population explosion and a renewed cycle for the intestinal parasite found in the bunnies, the whole process takes only 7 -10 years to occur.
another theory is since grouse ( in the east) feed primarily on aspen buds, they say the aspen will create a chemical that will build up in the birds system and eventually reach critical mass, where there is supposedly a massive die off or hatch failure from the chick being too weak to break through their shell.
there are a couple (thousand) theories floating about for the cycle but these are the two most popular that I am aware of. but you got to remember 99.99% of all the information on the cycle pertains to east of the cascades or further.
in another thread I mentioned I was keeping track of my western grouse encounters and would love to compare notes with anyone else interested or that may have some insight toward the western wa grouse cycle or if there even is one.
