TAILS WITH A DARK SIDE:  The truth about whitetail - mule deer hybrids

By Jim Heffelfinger

Author of the book “Deer of the Southwest”  visit his website www.deernut.com to get a copy.

The “Minotaur” of Greek mythology was a creature that was half man and half bull.  Hybrids have always fascinated us throughout the history of mankind.  Many of our monsters are a mixture of man and beast (Wolfman, Dracula, the Fly).  Likewise, consider our heros: Spiderman, Batman, and Cat Woman.  Our obsession with creatures that are half one thing and half another extends to our enjoyment of wildlife.  Early naturalists often described new animals as a combination of parts from animals already known to man.  The mule deer was described by John  J. Audubon in 1846 as having fur like an elk but hooves like a whitetail.         

Whenever hunters gather, there is always abundant talk about the types of deer from different areas:  Kansas whitetails, Montana mule deer, Sitka blacktails, Key deer, Coues deer, Carmen Mountain whitetails, fat Wisconsin does, and wide South Texas giants.  Despite all the differences across the country, there are actually only 2 species of deer in the U.S.: white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus).  The different-looking black-tailed deer of the pacific northwest is actually a type (subspecies) of mule deer. 

All native deer in North America are either mule deer or whitetails.  On rare occasions, however, we hear of a deer which can not neatly be labeled as one or the other.  This mysterious deer looks mostly like a mule deer but has a tail with a dark back-side like a whitetail.

Different species of animals, even closely related ones, are normally kept from breeding by being geographically isolated from one another, or by separating themselves into different types of habitat.  If the animals coexist in the same habitat then they generally have different courtship and breeding behavior to prevent interbreeding. 

In most areas of the West where both deer species are found, mule deer inhabit the higher mountain areas and whitetails occupy the lower valleys and river systems.  This habitat preference is reversed in the southwest where Coues whitetails are found in the mountains above 4,000 feet and the desert mule deer occupy the lower-elevation valleys and foothills.  Because of the interspersion of whitetail habitat (mountains) throughout mule deer habitat, the southwest has an extensive zone where the two species coexist.  This results in the animals being in close proximity to one another during the breeding season.  It is not uncommon to see a group containing both whitetails and mule deer in these areas of overlap. 

In the case of whitetails and mule deer, courtship and breeding behavior is different enough that body language and scent cues given off by a female mule deer during rut are not "understood" by a male whitetail and vice versa.  Also, in many areas where their range overlaps, the rut peaks at slightly different times for the 2 species.  This system of species segregation has worked remarkably well throughout their evolutionary coexistence.  However, in rare cases this system breaks down and genetic material slips across the behavioral barrier, resulting in a deer that is half whitetail and half mule deer.  This hybridization between the two different deer species is extremely rare but does occur throughout the West where their ranges overlap.

These bucks show characteristics which are intermediate between mule deer and whitetails.  Body size and facial features indicate a mule deer but the tail is usually dark chocolate brown or black on top and white underneath.  The tail of a hybrid looks very much like a typical whitetail, but is frequently much darker.  Ears are normally larger than a whitetail but smaller than a mule deer.  The preorbital gland in front of the eye is also intermediate between the deep pits found in mule deer and the shallow depression of whitetails.    

What about the antlers?  Forget about the antlers; this is a worthless characteristic to judge whether an animal is a hybrid or not.  Most documented hybrids have whitetail-like antlers but you can’t count on antlers alone.   I have 3 sets of antlers in my livingroom: 2 are whitetails with forked primary tines (G2) and the third is a desert mule deer with 8 long points, all arising from the mainbeam.  There is simply too much variation in antlers to serve as a reliable indicator of hybridization.  The whitetails in the Carmen Mountains of northern Mexico have been shown to exhibit a high degree of forked antlers like mule deer.

The best feature to determine if a deer is a hybrid is the size of the metatarsal gland, which is located on the outside of the lower portion of the rear legs.  This should not be confused with the tarsal glands on the inside of the legs.  The metatarsals on mule deer sit high on the lower leg and are 3 to 6 inches long and surrounded by light brown fur.  The whitetail's metatarsals are at or below the mid-point of the lower leg, usually less than 1 inch, and surrounded by white hairs.  A whitetail-mule deer hybrid has metatarsal glands that split the difference, usually measuring between 2-4 inches and encircled with white hair.   

Two year-old mule deer are most frequently mistaken for hybrids.  This is because of their smaller antler development and the fact that the dichotomous branching, producing the big "forks", usually does not occur until the buck is 3 years old.  Young mule deer sometimes give the appearance of a very large white-tailed deer, especially if it’s tail has a dark stripe down the back, as sometimes occurs.  Mule deer in some areas, like southern California, have a dark band running down the back of their tails.    

Hybrids have been reported from captive facilities as early as 1898 when a whitetail-mule deer cross was produced at the Cincinnati Zoo.  Occurrences were later reported from the Zoo in Minot, ND, deer pens in Alberta, and others.   Researchers in Tennessee also successfully produced whitetail-blacktail hybrids in a captive situation.

In the 1930s, biologists in Arizona produced hybrids by mating mule deer males to whitetail females and also whitetail males to mule deer females.  These matings resulted in 9 hybrid fawns, of which only 4 survived the first few months.  The research ended abruptly and the deer had to be released before any meaningful data could be collected.  In the 1970s, Gerald Day also produced hybrids in captivity in Arizona.  Ten hybrids were born but only 4 lived past 6 months of age.  Survival appears to be very low in hybrids even when pampered in a captive facility.    

Coues whitetail x desert mule deer hybrid (F1) produced in captivity by
Gerald Day in the early 1970s. Note the whitetail-like antlers and tail, but
intermediate metatarsal gland on the outside of the lower rear legs. Photo
by Gerald Day.

Survival in the wild is even more difficult when food doesn't come from a feed trough and there's no fence between them and animals with sharp teeth.  To complicate matters, hybrids inherit predator avoidance strategies from both types of parents; the problem is, whitetail and mule deer have drastically different techniques for escaping predators. 

The whitetail’s key to escaping is speed.  They put their head down, follow established trails, and try to put as much distance between themselves and the predator as possible, as fast as possible.  Mule deer, on the other hand, have developed a pogostick-like bounding called "stotting", where all four hooves hit the ground at the same time.  This strategy developed in mule deer because they evolved in wide open and rugged country throughout the West.  Their escape by stotting is not as fast as the whitetail's, but in rugged terrain it is effective for putting obstacles between the predator and the deer.  Mule deer can bound over boulders and stumps that the predator must run around.         

Research by Susan Lingle using captive animals in Alberta, has shown that stotting is so specialized that only deer that are 100% mule deer can do it.  Even a 1/8 whitetail X 7/8 mule deer fails miserably.  The hybrid's escape behavior is chaotic; the deer will typically approach the threat and jump around in confusion.  Such behavior is not conducive to passing their genes on to another generation.    

Whitetail-mule deer hybrids have also been reported in the wild from Alberta, British Columbia, Nebraska, Kansas, Colorado, Washington, Texas, and Arizona.