Yes they definitely migrate or just move toward food at least the gray squirrels here in eastern Ky. I've seen evidence of it several times. I was in one of my normal hunting areas not to many years ago, aprox 2010-11, can't remember for sure, sitting on a ground blind bowhunting deer. Had been there several hours without seeing any squirrels. Almost at once they were moving all around me, steady moving in one direction. Can't come close to saying how many different ones I seen, but many. This lasted probably 20-30 minutes and they were gone, no more seen rest of hunt. It was a bad year for acorns and beech nuts. I believe that same year they were all over some of the roads, many seen and killed, for several days, then nothing. My dad has seen this also, and it was a very noticeable and large scale one year in the mid to late 60's.