Jimmy, the answer to that is simple.
Mother nature!
Mother nature causes deer in different regions to have different "biological clocks".
This is to protect the young from being born too early or too late in the year.
The amount of daylight change it takes a southern buck to go into rut is more than a northern buck. This is because a southern bucks offspring isnt subjected to as harsh of winters. It can be said that deer in warmer climates have a "looser" clock. Because the time at which their young is born isnt as vital to their survival.
Different regions deer, have different "clocks". But they all work on the same basic principle. As light increases a buck begins to grow his antlers in spring. As the light begins to fade again, the shorter time of year, the buck has the urge to breed. This breeding takes place at the most opportune time, for the gestation period to conclude during spring. A time when the newborns will have plenty of food to begin growth before fall and winter set in. It works the same with bears, except that they have a delayed fertilization. Where the mother bear doesnt actually carry the young, until just before entering the den. This allows her to retain more nutrients for herself before "hibernating".
I understand why your doubting me, but its all been proven through science. You dont have to believe me, and some of it is hard to believe, but it is all relatively true. I have been studying deer biology since I was a young boy. Taking facts and research from different sources, and compiling them to sort for the truth.
If you have any more questions, feel free to ask! Have a good one---Matt
