Yarding behavior, when deer migrate to areas that can better sustain them through winter, is a complex annual phenomenon in the northern portion of the whitetail's range, so the answer is not simple. Some research from northern Minnesota and the Upper Peninsula of Michigan suggests that a prolonged period of cold temperatures (less than 20 degrees) can trigger such movement to yarding areas. There is a lot of variability in migration dates, however, as different family groups head to their traditional winter grounds at different times. An early onset of adverse conditions can accelerate their departure, and there is also some indication that nutritional levels or habitat conditions on the summer range can affect the timing. Bucks traditionally migrate later than does.