Defined QDMA style. - New article. What Triggers the Whitetail Rut? | Quality Deer Management Association
Without reading the article, I'm going to say that it is all determined by the decreasing amount of daylight. Days get shorter, testosterone rises, does get knocked up.
When a Mommy deer decides she wants to have a baby deer she goes out struting her stuff around with her tail up and that brings all the boys to the yard.