A lone hunter will see twice as many partridge as two hunters, yet two hunters will kill twice as many birds as a single hunter. Does any of that make sense? Let me scratch my head a minute. What about three hunters? Two dogs? Three?
Ruffed grouse, called partridge where I hunt, hear pretty darn well. The bells we put on our pointing dogs probably get their ruffs up a hundred yards or more away, but fortunately the birds are programmed to rely on their camouflage and hunker down, hoping that whatever is making that jangling noise just passes on by. A bird that can go from zero to rocket-speed in the blink of an eye has little to worry about as long as it can keep track of that sound. Add a second dog and there still doesn’t seem to be much worry for the bird. Apparently they can count well past two.
They don’t seem to be aware of the approaching hunter until he or she is very close, which is when they flush. Throw in human voices though and the bird’s nerves get rattled and flight seems right, hence an increased number of wild flushes.
Instinctively a fleeing grouse tries to put something between it and the peril, whether the danger is a pursuing goshawk or a tall strangely-dressed hunter. When the bird leaps into the air it already knows which tree it is going to duck around or knoll it is going over or softwood to dive into. One hunter with one prospective is relatively easy to avoid.
But two hunters, traveling silently, working with hand signals, positioning themselves to cover the partridge’s possible escape routes, and the bird’s odds of seeing another day decrease dramatically.