|Whitetail are the
oldest living species of deer at 3.5 million years old. The blacktail
deer ( Odocoileus hemionus ) split off
from the whitetail at some time in the past, thought to be a million years
ago or more. The blacktail and the whitetail are different species.
The blacktail deer then split off a subspecies, the mule deer (Odocoileus hemionus hemionus), which is the youngest living deer species, arising 10,000 years ago. So the blacktail and mule deer are the same species, but the mulie is a subspecies of the blacktail, and they are both close cousins to the whitetail.
Of course nothing is ever simple, and there is a complicated three way relationship, found by mitochondrial DNA evidence, that the making of the mule deer involved some crossing back of the whitetail to the blacktail deer.
The two species do not normally interbreed in a natural setting, but will if kept confined together. The hybrids do well in captivity, but in the wild they rarely survive because they do not know how to follow the successful survival strategies of either parent, and so are vulnerable to predators.
Blacktails range from Alaska and British Columbia in the north with the sitka deer and Colombian blacktail deer, down through the California mule deer, the inyo deer in the Sierras, the Rocky Mountain mule deer, to the burro (bura) deer of the southwestern deserts and Mexico. The ranges of the subspecies of blacktail overlap latitudes, but the blacktail deer exist no farther east than the Rocky Mountains. There are some other named subspecies of blacktail, but there is debate as to their validity.
An essential divide between the whitetail and blacktail species is their different choices of terrain and their different escape strategies. The mule deer lives in rough but open country and uses a special kind of pogo stick jumping as its main escape from predators. It is called "stotting". A single, springing jump can cover more than twenty-five feet! The mule deer will tend to pogo itself uphill when it escapes. This is a very different strategy from the whitetail who sprints, running downhill, using gravity to increase its speed, and thus often running to water. The whitetail hides, jumps only over obstacles, and prefers the cover of its well known home range in the woods, and prefers the terrain to be even so it will not slow down its sprint to safety.
When a mule deer stotts it is choosing a slower escape than if it galloped away. The jumping works better though for a few reasons: One is that the high jumping mulie can go uphill and it does not cost him much more energy than jumping on level ground. For the earth bound predator though, climbing uphill increases its energy output enormously. Another advantage is that the mule deer's territory is usually rough and uneven and it can match its jumps to the uneven terrain, sailing over obstacles that slow down the predator who has to climb over, under or around, and sailing over gaps that the predator cannot cross at all. A final advantage is the unpredictable direction of the jumps. Some people say that it seems like the deer itself doesn't know which direction it will bounce off to next, and this leaves the predator swirling in confusion, either unable to anticipate where to attack, or wasting huge amounts of energy on attacks into thin air.
Why don't you ever hear about mule deer in the South? There is a disease barrier between the climates that have killing frosts that eliminate certain parasites and disease carrying insects, and the year round milder climate of the South that does not. To put it simply, you do not see mule deer in the South, or for that matter moose, because we cannot keep them alive and healthy due to disease.
MULE DEER AND BLACKTAIL