I've seen that here in AL in mid summer also, when the fawns start to drop and mamma deer start to nurse. My logic is that mamma is now eating for two, herself and the fawn. Not that she wasn't before, but the fawn is now really growning and mamma needs calories. I have also seen big does that appear just about to drop (fawns) feeding mid day, terrible heat and humidity on soy bean fields, same concept, high protien chow down for her and soon to be newborn.
This is my theory, and I cannot substantiate with data, but I have seen many times and is the conclusion I have come to.