Texas Parks & Wildlife Magazine   


September 2009 cover image hunting dog

Mule Deer Mystique

New research hopes to provide better population estimates.

By Russell A. Graves

It won’t take long to get on one and get him caught,” predicts pilot Dusty Whitaker while his two-seater helicopter refuels behind us on the makeshift red-dirt tarmac. Just a short distance from the Caprock Escarpment and west of Matador, our impromptu command post includes the helicopter, a couple of ATVs and a cadre of pickups. Stretched out across the ground, bright orange catch-nets strike a peculiar contrast against the frost-killed grass, as a couple of Dusty’s helpers pack the nets into the rocket guns.

“Once I get in the air, y’all need to have your crew ready to move in and get the deer and I’ll take off and catch another.”

Dusty makes the process sound simple, but having seen him do the catch-on-the-fly routine once before, I know the aerial acrobatics involved in this research project are far from simple.

While he speaks, a collection of Texas Parks and Wildlife Department biologists, college students (both graduate and undergraduate) from West Texas A&M University and Texas A&M University-Kingsville wildlife management programs and their respective college professors gather around in a huddle to listen for the day’s agenda. In short order, various members of the group pore over maps of the ranch, delegate responsibilities for each crew member, and engage in jovial banter while Whitaker finishes his preflight routine.

The plan today is to catch 36 mule deer by day’s end and catalog things like their sex, age and rump fat thickness to gauge their overall health. In addition, before their release, the crew will adorn each deer with ear tags to aid in identification and a GPS collar that logs their latitude and longitude over two-and-a-half months before they automatically fall off the deer and are retrieved by researchers using radio telemetry technology.

It’s mid-December and the morning is overcast and predictably chilly by Texas Rolling Plains standards, but after hearing of the bevy of physical activity that’s to come, there is no doubt that covered up in the heavy coats and gloves, we’ve all overdressed.

Research in motion
After pulling up to an old barn that flanks a green wheat field on the ranch’s western edge, mule deer quickly shoot from the cow lot and across the wheat field. At first I am fixated on the deer hopping toward a newly erected wind farm in the distance. Instantly, though, the recognizable chop-chop-chop sound of the helicopter blades erupts from the brush and the black chopper rushes past, only feet from the ground. Over the wheat field, I see an orange net open swiftly from beneath the aircraft’s blades, and a puff of dust confirms that the first deer is caught.

In a smooth and choreographed fashion, the ground crew moves into action and sidles alongside the netted deer, loads her onto an ATV, and brings her back to the barn, where graduate research assistant Cody Zabransky helps coordinate the ground work under the guidance of his major professor, Dave Hewitt. Cody is here working with Texas A&M University-Kingsville under the Caesar Kleberg Wildlife Research Institute and is instrumental in the mule deer research project.

On the ground, the deer get worked over in a humane fashion. Their eyes are covered to calm them, and their feet bound to keep them from hurting themselves or the researchers. While does can injure with their flailing feet, the bucks are handled especially gingerly to avoid any damage to their antlers and keep their antlers from impaling a researcher.

While one researcher ear-tags the deer, another shaves a patch of hair from its rump so an accurate ultrasound can be administered, and yet another records all the pertinent data marked by the various data collectors. In the end, whoever has the small digital camera at the time photographs the animal before it’s released.

ear-tagged mule deer

Back on their feet, most deer react the same way to the global positioning system collar and the ear tags, curiously shaking their heads while trotting off. Soon though, they become accustomed to their regalia and carry on as mule deer do. While it seems like a lot of work just to figure out more about mule deer, when it comes to this project, there’s much more to it than simply what I’ve witnessed.

“The purpose of the research is to develop a sightability model for aerial surveys of mule deer in western Texas,” explains Zabransky. “The Texas Parks and Wildlife Department currently uses data counts that do not estimate population levels, but instead provide population trend data.”

According to Zabransky, when subjected to scientific scrutiny, the current method of counting mule deer employed by TPWD is highly variable and not as accurate as needed for critical population and habitat management decisions. Overall, the research assesses how the effects of terrain, vegetation type, woody cover, weather, deer activity, group size and observer experience influence sightability of mule deer during helicopter surveys. Researchers admit that the percentage of deer observed during helicopter surveys is not known, and the percentages often vary due to a number of variables like brush cover or weather at the time of the survey.

Determining the actual number of deer on a range is a challenge using current techniques, and according to Calvin Richardson, desert big game leader with TPWD, spotlight survey results are often inconsistent due to the limited road systems on some West Texas ranches. Moreover, current aerial survey techniques typically underestimate deer numbers.

“The ultimate goal is to possess the ability to ‘correct’ our estimates following a helicopter survey under a specific set of conditions,” says Richardson from his base in Midland. “More accurate population estimates at the state and ecoregion levels improve our ability to manage the mule deer population. Accurate data improves our decision-making ability regarding seasons and bag limits, as well as for any other proposals that may arise in the future, such as managed land deer permits or antler restrictions.”

In this particular research study, trapping takes place on six different ranches in the Texas mule deer range. Two of the ranches are in the Panhandle, while the balance are in the Trans-Pecos. Each ranch is big enough to ensure that the census methods developed from this project are applicable over the entire mule deer range.

“Mule deer are the focus of the study because they require a model of their own, as a model developed for white-tailed deer would not apply to mule deer because of different habitat types and behaviors of the two species,” Zabransky notes.

Dry country drifters
As far as Texas deer, the desert mulie is the less-common cousin of Texas’ most prominent deer — the whitetail. Because its range is found in the least populated regions of Texas, many people aren’t as familiar with the deer that roams chiefly in the Texas Panhandle and the mountains and basins of the Trans-Pecos.

Historically, mule deer resided in nearly every Texas county west of the 100th meridian. By the middle part of the 20th century, over-hunting and habitat changes reduced their range substantially and pushed them into the desert mountains of western Texas and tiny pockets in the Panhandle.

Currently, because of a trap-and-translocate program that ended in 1988 and stricter adherence to sound habitat and population management philosophies, their numbers and range have expanded. The Trans-Pecos holds about 85 percent of the statewide mule deer population.

In body size, mule deer are slightly larger than whitetails. The first thing you’ll probably notice is its large namesake ears that resemble those of a mule. Typically, as mule deer bucks grow larger, their antlers branch dichotomously fork, as opposed to a white-tailed deer, whose tines grow typically from a single main beam. While whitetails generally are found in the wetter and densely vegetative habitats in the eastern two-thirds of Texas, mule deer occupy the drier open country and range over as much as 10 times more area than whitetails.

Because of the inherent differences in white-tailed and mule deer, management strategies vary between the two species. Therefore, from a wildlife management point of view, several concerns arise with the management of Texas mulies.

“Intensive supplemental feeding is becoming a management concern from the perspective of most deer biologists,” advises Richardson. “With good intentions, many managers provide year-round high-protein feed to prevent drought-induced fluctuations in deer numbers, and some provide feed to increase antler growth in bucks.”

Richardson says that supplemental feeding typically benefits mule deer herds the first few years by inducing greater body weights and slightly larger antlers, but invariably, fawn production and survival increases to as much as 80 to 90 percent, and many fed deer herds triple or quadruple in numbers within the first 10 years.

“Since most managers are reluctant to harvest mule deer does, long-term overpopulation is inevitable. What most managers don't realize is that the feed composes only a small portion of the overall diet, and the majority of a deer's diet consists of native vegetation,” Richardson advises. As overpopulation occurs, the highly preferred native plants are affected first by the browsing pressure, and the habitat experiences long-term decline, which ultimately reduces the carrying capacity of the land for deer and other wildlife, he says.

“Overall, the mule deer herd in Texas is in great shape due to the management efforts of private landowners in West Texas. Compared to other southwestern states, desert mule deer harvested in Texas tend to be more mature than in other states that have more public land, and sex ratios in Texas are tighter than in other states due to the conservative harvest of bucks in West Texas.”

While Texas mule deer are doing well, that doesn’t mean a hands-off management approach should be the rule. Instead, the catch-and-collar research is not only used to establish more scientifically sound census methods, but researchers are learning more about the western Texas deer and their habitat utilization. Additionally, because of the more accurate population data to come, this research goes far in helping private land managers make sound management decisions on a local scale.

“Biologists have long recognized that a certain proportion of deer are missed during aerial surveys. A few deer are usually missed because mule deer are good at blending into their environment when they don’t move — especially on overcast days,” Richardson confides. “It's likely that the majority of deer that are missed are not even visible to the observers — like when they are standing or bedded in woody cover or rugged terrain. This research will ultimately help us to account for those deer that we've been missing.”

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