Deer are seasonal breeders which means they begin mating in the cold and harsh weather. Does go into "heat" which is when they produce estrus, this lets the bucks know when they are ready to mate. The "rut" is the breeding time, the peak of the rut is middle to late November to early December. During these cold and harsh months the bucks begin to fight using their antlers for dominance and territory. These fights can end up in death by stabbing one another or getting their antlers locked together. The gestation period of a mule deer is 195-212 days. If you hunt deer this is the main time to get in the woods because bucks only have one thing on their mind and you can get in close. The most common way to tell the difference between a buck (male) and a doe (female) is bucks have antlers, they are typically bigger bodied too. Typical life span in the wild can be up to 10 years, not every deer lives to be that old due to predators and disease.