Most hunters are surprised to learn that the natural mortality rate of mature whitetail bucks is 10 - 30 % by natural causes.  These numbers do not include death by hunting. 

Surprisingly, while predators like coyote and mountain lion are responsible for some deaths, the implementation of strong predator eradication programs do not play a significant part in keeping bucks alive. 

The highest mortality rates are with young and old bucks.  The post-rut period between January and March realizes almost 80% of these deaths which can be attributed to poorer nutritional supplementation following the rut period.  During the rut a buck may lose up to 30% of his body weight and not have proper nutrition available until spring in which to gain back the lost pounds.  During this weakened physical condition these animals are also the most susceptible to predators.

One study of buck mortality showed that with a beginning herd of 100 6 month old bucks, only 24 of those bucks lived to the age of 6 1/2 years old.  These bucks that died were all of natural causes as these bucks were not subjected to hunting at all.  That means that without any hunting pressure, 76% of bucks will die before reaching full maturity simply by natural causes.