A week or so ago was able to spend a little time with Al Stewart, Michigan's Upland Bird Specialists at a seminar put on by RGS.
Sounds like the concern is that WNV may be more lethal for grouse than for pheasants or turkey. Michigan hopes to test several hundred grouse this fall (thru cooperative hunters) to try and get a better handle on this.
12 Michigan grouse were found to have died or serious ill from WNV last fall. And these were birds that were just turned in by concerned citizens.
Until the results are in, Michigan hopes that good habitat will make for healthy grouse which can better with stand the disease. So their hope is by improving habitat the birds can get past this. But a few years of sampling will be needed.
How many died from it and were never found ?