Hey 160user,
One of the reasons last fall was such a banner year was all the snow we received. Snow is a much better insulator against the cold than other roosting cover (often 30 degrees) as well as providing far more protection from predators. It has little impact on food sources as winter foods are overwhelmingly aspen and alder catkins in the north. That the winter was followed by a dry spring during and immediately following the hatch was greatly helpful. This year I have some concerns as the snow cover was so much less making predation higher. At least there wasn't fridgid weather to worsen the mix.
The greatest problem is lack of habitat, or maybe a better description would be changing habitat. Many believe there is not a problem on that front as they see plenty of forests but they only see the obvious and not the details. Our aspen forests are aging as the pulp industry has crashed. Many mills have closed in the last three decades and the remaining ones are not as busy. That means the aspen woods are older and less grouse friendly overall. An aspen woods needs to be logged about every 40 years of which maybe 15 are prime for grouse hunting. With the collapse in pulp prices about 20 years ago what habitat out there is rapidly aging beyond its prime. This aging is not helped by an increase in private land ownership of whom the majority are loath to have their properties logged or otherwise managed for grouse. This leads to another problem - changing forest types.
In Minnesota the classic grouse cover is early to mid-growth aspen woods. With the lessened logging that is turning into maple/basswood/oak type forests. This is not a good forest type for grouse though those who only recognize there are trees present would think it good habitat. I own/manage a couple sections of land in northern Minnesota and I have noticed that the oaks that were present have increased in number and maples, ash, basswood, and the like have become present. This in spite of a regular logging program for over 4 decades. Further south and the numbers of these "interlopers" are even more noticeable.
A final issue is fragmentation and access of lands. Private cabins and other uses has lead to a change in forest densities and utilization. This may not be readily apparent to many but an acre or two here and a couple more there add up in the grand scheme of things. This can be difficult to see from aerial photos but actually getting up in a plane every year and observing the ground can be eye opening. Access is another consideration. In the last 30 years the use and popularity of ATVs has grown tremendously. These vehicles allow ready access into areas that were once rarely accessed by hunters. These formerly inaccessible areas were kind of refuge areas where excess birds dispersed from and into more used areas. Now, hunters on ATVs access areas in minutes that took hunters on foot hours (if ever) to get to. This puts a strain on what were once surplus birds that repopulated more heavily hunted areas.
Disease can also be an issue as can predators but those can be mitigated to a fair extent with habitat. If a combination of these two factors kill 60% of the population per year then prime habitat that yields 50 birds will have more to carry on than poorer habitat that yields only 20. Predators having a significant impact on populations are more a sign of poor habitat as predators have been around for a good long time. Our prime grouse areas are rife with predators but the quality and quantity of the forests have been able to allow grouse and other animals to handle predation.
What it really boils down to is habitat. One needs both quality and quantity to maintain a population. With both one will have high populations of the given animal. Lack one or both and populations will plummet.
