The mule deer is a deer indigenous to western North America; it is named for its ears, which are large like those of the mule. There are believed to be several subspecies, including the black-tailed deer. The most noticeable differences between white-tailed and mule deer are the size of their ears, the color of their tails, and the configuration of their antlers. In many cases, body size is also a key difference. The mule deer's tail is black-tipped, whereas the whitetail's is not.