Ruffed Grouse

[bassnpro1]

This is and has been a topic for many years. My relatively educated guess is that the real answer is a combination of factors, and that pointing a finger at any one thing will 100% miss the mark. Factors that I have heard legit biologists talk about in various regions:
1) west nile virus or another avian disease.
2) habitat loss (early successional growth from farms abandoned through the mid 20th century that are now either subdivisions, pole-size or bigger timber, or fence-to-fence agriculture, or also from loss of widespread beaver activity that created much of the naturally-occurring habitat)
3) the internet. Seriously. Much of the upper midwest and NE timber market was driven by the pulp wood market, and we all know how newspapers and paper book sales are doing—in the toilet. Timber companies are selling off their land and becoming real estate companies in many areas, and for private or public landowners/managers cutting to maintain grouse habitat is now a $-losing proposition most of the time.
4) lack of habitat connectivity (grouse brood dispersal relies on having widespread good habitat, not just pockets of good habitat)
5) return of predators, both ground and avian
6) warmer or shorter winters with less opportunity for snow roosting
7) invasive species like honeysuckle, buckthorn, barberry, knotweed, etc that displace native vegetation that has higher-value nutrition and cover.
8) expectations—if your expectation is an unnatural super-abundance of birds caused by a “perfect storm” of factors through the mid-late 20th century, its likely that outside a unique situation like that its just not gonna happen again.

Quite an extensive list. I can't argue with any of those, but I would add one.

9.) Ticks. My area of Ohio went from having almost zero blacklegged ticks to now being infested. I took a walk through grouse habitat two years ago on Dec 29th and pulled 38 just off of myself. I would imagine they would suck a young grouse dry if they had to deal with them every single day of their life.

[MacIntosh]

Same here. 15 years ago I would hunt all day in thick brush, and never found a tick on me or the dogs. These days I’ll go into one cover in the lowlands and pick 20 or 30 ticks off. It’s not as bad as some places, but the change from zero to what we have now in just a decade or so is downright shocking. Grouse will eat ticks, so I’m not sure if they help or hinder, but I have seen some research suggesting that certain invasive plant species increase the prevalence of ticks, so whether it’s a cause or not, it may be correlated with some of the other factors. Luckily, the higher elevation areas around me where I still grouse hunt there aren’t really many, if any, ticks yet.

[MacIntosh]

The other factor is that in many areas of the country grouse populations naturally cycle with avian predators. The standard line is that grouse populations go on a seven-year cycle. I haven’t seen that around me nearly as much as in the upper Midwest, but it could have something to do with it for sure.

[stosh]

haven't seen a grouse in about 7 years

[jigheadworm]

Lack of clearcuts affects grouse. Back when there where lots of clearcuts grouse where abundant around them, now no cuts have been made epecially on gov land around here.Cuts give them cover and food. Open woods is a death sentence for grouse from predators.