I identify white-tail and mule deer, either confirming a species ID or adding a species ID to an ob identified to genus or higher. Sometimes there’s only scat, footprints, or bones, and all I can do is annotate it to get the attention of scatologists, ichnologists, or osteologists. If there’s an animal, I look at these:
Mule deer have a black or at least black-tipped tail; white-tail deer have, of course, a white tail.
Mule deer’s ears are bigger; that’s why they’re called that.
If they have antlers, they branch differently in the two species. But I’ve seen at least one with velvet antlers that were just at the first bifurcation; at that stage, I couldn’t tell.
I’ve also noticed that some deer have a black border on the ear, but I’m not sure which species, or if it is a specific trait. What else should I look at?
I’m in New Mexico and Mule Deer are much more common than White-tailed but I’ve photo’d both here. We even have evidence of hybridization of the two species in the southeastern part of the state.
One characteristic I’ve noticed in the absence of antlers or a clear view of the tail is that the body proportions appear to be different. WTD seem to have a larger body in relation to head size. They also have more white around the snout and face. Just generalities … I’d have to study photos more to be more descriptive than that.
This is a detail that mainly helps with identifying a hybrid between the two species as being the most reliable, but it also works to identify either species. The metatarsal glands that you’ll find on the legs are one of the most reliable features to look for. Mule deer have larger, brown glands and whitetails have smaller, white glands, and if it’s an intermediate between the two in some manner, it’s a hybrid. This does work best with having the other main features like the tail, ears, facial markings etc, but when it doubt, look at the glands.