I don't know about that. Every morning there is a whole flock of pine grouse (ruffled grouse) sitting in one or another of the ornamental apple trees around my house and yard. As soon as I look out the window at them and notice they are there they all bugger off. I could be on the couch 10 feet away from a window, not move a muscle, just my eyes, and they either blast off or freeze up solid, ready to blast off. It's amazing just how sensitive they are. You'd think they'd be used to me by now, and I never hunt them to make them leary.
This flock has existed around here for about 15 years now, (the original birds offspring now of course) and they always seem to maintain a healthy number of about 25 birds or so that survive the winter.
I suppose many of the spring chicks fly off elsewhere in the fall; (they usually have have 2 hatches during the summer of about 10-15 chicks each female) I've often seen some scooped up by owls and coyotes, or find a pile of feathers here and there, but out of the hundred or so that literally infest my forest in the fall, (I have a 2500 acre spread of which about 1500 is forest) there always seems to be a group of 25 or so that hang around all winter eating from the fruit trees in my yard site.