A Look At Whether or Not Whitetails Are to Blame for the Decline
By: Realtree Staff
“Go West” was 19th century publisher Horace Greeley’s advice, and now, more than a century later, it appears North America’s whitetails may be heeding that same advice. The prolific and adaptable species is expanding into areas once the primary domain of the mule deer. And where it’s occurring, there’s concern that whitetails are displacing mule deer.
Historically, whitetails and their various regional subspecies inhabited roughly the eastern two-thirds of the nation, plus areas of Canada and Mexico. The mule deer’s range was primarily the western portions. Whitetails were deer of the lowlands, gently rolling hills and forests. Mulies were primarily present on the West and Southwest’s plains, semi-arid deserts and in the mountains. Where the two species’ ranges overlapped, they still tended to remain separated by habitat preferences — mulies to the higher ground, whitetails to the lower ground. But about the mid 1950s, wildlife biologists began to study the species’ impact on each other where the two ranges merged.
Mule Deer in the Beginning
According to the Colorado Div. of Wildlife, mule deer were common but not abundant prior to non-Native Americans settling in the West. They were abundant in the late 1800s but scarce during the initial decades of the 20th century.
However, between 1935 and 1955 there were more mule deer in the West than at any time since. Subsequently, mule deer numbers have historically fluctuated, primarily in response to climatic and habitat conditions and the effects of hunting. However, in general, their numbers have been declining at least since the late 1950s. Today, mule deer populations in Colorado may number less than half of the peak populations of the recent era.
Heavy browsing pressure, combined with conversion of habitats to other land uses, may have lowered the carrying capacity of current mule deer habitats to the extent that they now are not capable of supporting historic numbers. Also, when populations reached their most recent peak, in the 1940s and ‘50s, reaching maximum carrying capacity in many areas of their winter range, such as in Colorado and Utah, wildlife management reacted to control their numbers. Increased depredation to crop and grazing lands by the abundant mulies motivated wildlife managers to push for larger harvests by hunters, and that, along with changing land-use preferences gradually brought the population down.
Why the Decline?
Factors causing the ongoing decline in mule deer numbers in Colorado and elsewhere are largely speculative. Available evidence suggests that important mule deer habitats have deteriorated through time and that the current capacity of those habitats to support deer is now lower. Habitat effects could be amplified by increasing elk numbers, disease, predation, and hunting, but no large scale herd study results have been conclusive.
Since mule deer numbers have fluctuated historically — due to human pressures, conversion of deer habitat, suppression of fires that create food availability, and increases in exotic plant species—the current decline might be looked at as cyclic. But that may not be the case. Both domestic livestock and elk herds compete with mule deer for habitat and food. As habitat has changed, ideal mule deer range has shrunk, and competition with elk and livestock has reduced available food and habitat even further, while habitat more suitable for sustaining whitetails has increased.
Researchers at Colorado State University's Natural Resources Ecology Laboratory have found wildfire suppression is a factor in the decline of quality habitat and food supply for mule deer on the Western Slope of Colorado. Mule deer prefer plants that are close to the ground—grasses, wildflowers and low shrubs. When trees and dense shrubs become overgrown, they compete with plants that mulies prefer to eat, eventually changing the composition of plants in important mule deer habitat. In the past, natural fires had cleared deer habitat of trees and shrubs, which were replaced with new vegetation, thus creating a beneficial and plentiful food source for the mulies.
Land-use changes that negatively affected prime mule deer habitat could be one of the factors in the species decline — and the whitetail’s increase. Studies indicate whitetails will out-compete mule deer for available resources (food and cover) in most crossover habitat types. They can also occupy the similar habitats and have similar food preferences, but — and this is a big but — whitetails are more adaptable and aggressive than mulies. Whitetail bucks will breed with mule deer does, and the offspring usually retain the whitetail characteristics. Reverse mating — mule deer bucks to whitetail does — is rarer. So where the two species share a common range, the whitetail tends to dominate. And as habitat gradually changes to favor the whitetail, the mule deer becomes increasingly pressured.
How the Whitetails Win
Whitetails have more resistance to various parasites and diseases such as brain worm. They are, in fact, carriers of many diseases that mule deer are highly susceptible to. They also present a bigger management challenge to wildlife managers. Due to their elusive and nocturnal habits, they are more difficult to control in agriculture depredation conflicts and present a costlier management plan. Whitetails also have a higher reproductive rate, due to the fact that whitetail doe fawns can and do get bred in their first fall, before they’re a year old.
Mule deer are being displaced by whitetails on several different ranges, such as the lower elevations of the Southwest, the eastern plains of Montana, the Snake River plains and the Blackfoot Indian Reservation in Idaho, and in several locations throughout southwestern Canada.
What's the Upside?
A side benefit of recent reports of declining mule deer numbers and their shrinking range is that trophy mulie bucks — once considered easier to harvest than trophy whitetail bucks — are now being steadily elevated to a higher stature on today’s big game hunting wish list. And hunting in areas where the two species exist offers us the opportunity to take either a nice mulie or whitetail. That’s an attractive option to consider.
However, before we get too involved and concerned about the status of either species’ range, we need to keep our collective fingers crossed that the chronic wasting disease (CWD) that has caused so much concern is brought under control. For, unlike habitat or terrain, CWD plays no favorites and can infect and spread through either species.
Editor’s note: This was originally published in 2003.