More Water for Mule Deer?

Researchers release a mule deer doe after bring outfitted with identifying ear tag and high-frequency VHF radio collar.

NPS Photo: Kelley Stewart

 

Do mule deer in Mojave National Preserve need more water? It may seem like a silly question. After all, it’s a desert—doesn’t everything need more water? Scientists at Mojave National Preserve are working with the California Department of Fish & Game (CDFG) and researchers at the University of Nevada-Reno to answer this question, and a few others.

 

NPS Photos: D. Hughson

Government Holes (top) and Petit Well: artificial water sources in Mojave National Preserve.

Seeps, Springs, & Stock Tanks
Many people may be surprised to learn that there are many natural seeps and springs in Mojave National Preserve. However, the amount of water available to wildlife may vary from year to year. One component of the project is aimed at determining how annual rainfall affects the availability of water for wildlife at natural springs. Some springs, such as Piute Spring, flow year-round, while others dry up after too long a time without rain. National Park Service employees and volunteers monitor these water sources each fall to find out which springs are producing sufficient water to support wildlife.

The second part of the project focuses on learning more about the behavior of Mojave’s mule deer. For starters, no one knows for sure how the population size is changing. Deer have been hunted in the area since 1958. Since Mojave National Preserve was established in 1994, the average annual buck harvest has increased 50 percent, from 28 to 42 bucks per year. But buck harvest information alone is not a reliable indicator of mule deer population levels. 

In addition to springs, there are also stock tanks fed by wells throughout the preserve, principally (and historically) used for watering cattle. It’s not known which of these water sources deer used regularly, or whether they depend upon such artificial water sources of survival. Furthermore, is it water availability that limits the number of deer, or is it something else, such as food availability or predators?

 

NPS Photo: Kelley Stewart

A mule deer buck wearing a VHF radio collar.

Where the Mule Deer Roam
To learn more, up to 80 deer will be captured, tagged and released. In January 2008, the first eighteen deer were trapped and transported to a field site where researchers and volunteers efficiently gathered data: blood samples were collected; does were checked for pregnancy using ultrasound; weight, temperature, and other tests were conducted as quickly and safely as possible to minimize trauma to the animals.

Then, the mule deer were released into the wild, adorned with new accessories: two identifying ear tags and a VHF high-frequency radio collar. Some deer were also outfitted with an additional collar containing a GPS unit. After 375 days, the GPS collars automatically fall off. Analysis of the device offers researchers “hoof-by-hoof” intelligence on where the deer roam.

 

NPS Photo

Mule deer photographed while utilizing a spring in Mojave National Preserve.

Over the next several years, University of Nevada-Reno graduate students and National Park Service employees will monitor their movements several times a week. Cameras installed at springs throughout the preserve will also capture individual deer movement. When a doe stops for a drink, the camera photographs an image of her numbered “earring.”

Mule Deer Management: It Affects Us All
With this information, researchers and managers will be able to determine which of the springs and stock tanks in the preserve mule deer prefer. They might also be able to better characterize the physical and behavioral responses of mule deer—i.e., pregnancy rates, survival rates, and changes in population density and weight, etc.—to manipulation of, or changes in, water resources. In the future, managers will have much more information to use when making decisions that might affect Mojave’s mule deer. And this, of course, is a topic of much interest to hunters, scientists, and everyone who enjoys desert wildlife.

To learn more about the legislative and management history behind this research and/or to review technical documents, click here.