Research has suggested that mule deer may be the result of cross-breeding between whitetail and blacktail deer. Easily recognizably features are large, mule like ears and narrow, black-tipped tails, along with their typically dark gray coats. Mule deer can grow to about 125-250 pounds and stand 30-40 inches high. Mule deer inhabit most of the Western United States and Mexico, although some can be found as far north as Alaska. The most abundant subspecies of mule deer is the Rocky Mountain mule deer. This subspecies has large antlers, a darker coat, and lighter colored tails.
In total, there are about ten recognized sub-species of mule deer. However, the differences between them are so trivial (body size and tail color) that researchers argue if it is enough to establish another category.
Mule deer, like blacktails, tend to be more subdued than whitetails. When approached, Mule deer are more cautious, while the whitetail is quick to turn and run. Breeding habits also differ between the Mule deer and whitetails. A male mule deer's face closely resembles that of a fawn. Thus, a buck will court a doe by making fawn sounds and approaching her slowly; unlike the whitetail, who engages in a long chase.
During breeding phase, young male mule deer utilize an interesting trick in order to win a mate. When they spot an older buck with a doe, they will run at them as if avoiding a predator. This action typical forces the older buck and doe to also run in fear of the predator. The younger buck will then chase the doe. This behavior is unique to mule deer."