From the autumn equinox forward, day length shrinks every 24 hours. The pineal gland in a whitetail doe converts that change into a melatonin signal, which down-regulates reproductive suppression and brings the doe into a series of estrus cycles. The first estrus typically lands in the first half of November in the Upper Midwest, the second half of November in the Mid-South, and December–January in the Deep South. Latitude shifts the date because day-length change tracks latitude.
Bucks respond reactively. Their testosterone has been rising through October as antlers harden and bachelor groups break up, but the trigger for actual chasing-and-breeding behavior is the scent of estrous does. As soon as the first doe enters estrus, mature bucks pick up the cue and begin cruising downwind of doe bedding areas — that's the seeking phase.
Weather, food availability, and hunting pressure modify how visible all of this is, but they don't move the underlying biology. A warm year doesn't delay rut, a cold year doesn't accelerate it, and a poor mast year doesn't shift breeding dates — it shifts where breeding happens.
For the photoperiod-locked dates in your state and DMU, see our rut date pages.