Learn about threats to mule deer herds
Three mule deer, huddled together in a field, staring at the camera Three mule deer, huddled together in a field, staring at the camera

Learn about threats to mule deer herds

Weather, urbanization, invasive plants, wildfires and unmanaged grazing

Extreme weather can hurt herds and habitat.

Weather plays an important role in the health of Utah deer herds. Yearly differences in precipitation and winter severity cause fluctuations in herd numbers. Droughts and harsh winters can take a heavy toll on mule deer.

Harsh winters

Even under the best conditions, mule deer lose weight during the winter. During severe winters — with deep snow and prolonged cold temperatures — deer can lose too much weight and die. Fawns are the most vulnerable under these conditions, followed by older bucks and then does.

Stress during winter is another major factor in mule deer mortality. If a deer hasn't foraged on nutrient-rich vegetation, it has a hard time surviving deep snow and cold, especially when chased by predators or people.

Starting in early December each year, the DWR monitors individual mule deer herds on a weekly basis. Biologists look at both the deer and their winter range, assessing the following factors: snow depth, area temperatures, availability of forage, body condition (fat measurements) and depredation issues. If the deer fall below certain pre-established thresholds in three or more of these categories, the DWR is prepared to begin a supplemental feeding program to help them through the season.

Drought years

Mule deer also suffer during times of drought. A drought depletes the water that nourishes the plants deer need to survive. It also dries up areas where deer traditionally obtain drinking water.

To help deer and other wildlife during times of drought, the DWR has built and installed devices called guzzlers. Guzzlers gather rainwater and funnel it to an underground storage tank. From the tank, the water is piped to a drinker that provides animals and birds access to a cool drink. Many guzzlers are built in washes or gullies and take advantage of the natural terrain to capture rainwater. They may be all but invisible to the human eye, but guzzlers are well known and used by local wildlife.

Over the years, the DWR has built hundreds of guzzlers throughout Utah. Most were paid for with state habitat funds and contributions from conservation groups, including Sportsmen for Fish and Wildlife, the Rocky Mountain Elk Foundation, the Mule Deer Foundation, the Utah Chukar and Wildlife Foundation and others. County governments have also provided funding and assistance. Without these organizations' contributions, construction of many of these guzzlers would have been impossible.

Urbanization fragments rangelands and migration paths.

On average, the populations of the western states have increased by more than 25 percent during the last 10–15 years. Thousands of acres of rangeland have been converted into ranches, housing projects and industrial parks. In the entire United States, as much as 1.5 million acres of rangeland per year may be lost to urbanization. This growth has a direct impact on mule deer winter ranges and migration routes.

Homes on winter range

Much of the traditional winter range along Utah's Wasatch Front is considered ideal for building a home. The foothills — which allow many homeowners a spectacular view of the valley — are often situated in the heart of critical winter range.

During the winter, deer move from higher elevations down into many foothill neighborhoods, looking for forage that no longer exists. As a result, they sometimes eat homeowners' high-priced landscaping. Fortunately, there are options for homeowners who want to minimize browsing damage from mule deer.

Fragmented migration routes

Development on winter range has also fragmented deer migration routes. If deer have to cross one or more roads to reach high-quality forage, they run a greater risk of being hit by cars and trucks.

In many areas, the DWR has worked closely with the Utah Department of Transportation to build wildlife-crossing structures near busy freeways. These allow deer to reach critical ranges without having to jump fences or risk death on the road.

Invasive and old-growth plants pose hazards.

Utah's sagebrush rangelands are losing ground to cheatgrass and other invasive plants. These plants reproduce quickly, outcompete native vegetation and pose a huge fire hazard. They do not provide high-quality forage for mule deer.

Other plants are native to Utah — and may provide good cover for mule deer — but they have grown old and overtaken rangelands. Now, they crowd out the native shrubs and sagebrush that mule deer need to survive. They also provide fuel for raging wildfires.


Cheatgrass, a non-native annual grass, has moved into most of the sagebrush stands in Utah.

Cheatgrass establishes itself in the fall and winter, robbing moisture and nutrients from the soil when native grasses and forbs are still dormant. This early activity by cheatgrass has two main effects: it limits the growth of native plants, and it prevents the establishment of their seedlings.

By June, cheatgrass is ready to burn and often ignites with the first lightning strikes of the summer.

Unlike the more-isolated native bunchgrasses, cheatgrass creates a continuous cover of highly flammable fuel. Areas that were once sparsely vegetated and fire-resistant are now dense, dry tinderboxes. When ignited, wildfires spread through cheatgrass-dominated landscapes quickly and completely, consuming a much larger area.

The cheatgrass invasion has done more than just increase the acreage burned annually in the West. It has also dramatically changed the fire frequency. In cheatgrass ranges, fires occur every 10 years or less. In fact, cycles as short as every four years are common in cheatgrass-infested areas. Before cheatgrass invaded, fires occurred every 30–75 years, on average.

The increase in fire frequency has eliminated most shrubs and reduced the density of native bunchgrasses and forbs. As a result, the native plant communities that support Utah's mule deer herds are being wiped out at an alarming rate. Any native-plant communities in a cheatgrass/fire-dominated area have virtually no potential to be restored to their native condition without active restoration efforts.

To combat this problem, Utah's Watershed Restoration Initiative has taken the lead role in reseeding burned areas with plants that will reduce the intensity and frequency of future fires. Many of these plants are also competitive with cheatgrass and will limit its growth on Utah's rangelands.

Old-growth pinyon pine and juniper trees

Utah juniper and pinyon pine trees cover about one-third of the state. Both types of trees tend to crowd out desirable browse plants for mule deer.

In the absence of natural wildfires, decades-old plants — such as pinyon pine and Utah juniper — have increased in density, greatly increasing the risk of catastrophic wildfires. Some of these large, older plants are necessary to provide cover for wintering mule deer, but many of the plants have spread into sagebrush habitat.

To address this problem, Utah's Watershed Restoration Initiative funds and performs numerous lop-and-scatter (tree cutting), brushhog, chaining, controlled burn and reseeding projects. These projects remove the old growth and plant seeds to grow a variety of beneficial vegetation.

In many areas, there are now better watershed conditions; increased growth of shrubs, forbs and grasses; and more year-round forage for mule deer.

Intense wildfires destroy rangelands.

Every summer, Utah grapples with intense, widespread wildfires. Rangeland fires are now twice as common as they were in earlier centuries.

In 2007, the state experienced its largest recorded wildfire. During the nine days it raged, the Milford Flat Fire destroyed more than 363,000 acres.

Fueling the fires

Why is Utah burning? The primary culprit is cheatgrass. Not native to North America, cheatgrass has invaded our natural areas, and it spreads rapidly. This happens because cheatgrass:

  • Grows faster than native plants and monopolizes both water and nutrients.
  • Remains relatively unaffected by wildfires, coming back even stronger the following year while native plants struggle.

Dense stands of cheatgrass ignite easily, and fires spread quickly through the grass. It's a cycle that we are beginning to break, as we step in and set a new course for Utah's rangelands.

Rehabilitating fire damage

In the wake of the 2007 wildfires, Utah's Watershed Restoration Initiative spearheaded a multi-agency rehabilitation effort. Together, the agencies restored more than 285,000 acres of burned habitat.

As part of the restoration, the burned terrain was seeded with a mix of plants that will reduce the intensity and frequency of future fires. Many of these plants are also competitive with cheatgrass and will limit its stranglehold on Utah's rangelands.

Fighting future fires today

In addition to rehabilitating burned habitat, Utah's Watershed Restoration Initiative is taking preventive measures in many areas. The partnership plan projects cooperatively across landowners' boundaries to ensure a consistent fire-prevention effort. Most of these projects involve seeding, mechanical treatments and improved land management.

Some fires are necessary

As damaging as frequent fires can be to native plant communities, the complete absence of fire can have similar consequences. Without periodic fires, older sagebrush and pinyon-juniper growth can completely dominate landscapes.

Well-intentioned fire-suppression efforts by state and federal land-management agencies over the last 50 years have changed our rangelands. Without periodic lower-intensity fires, pinyon-juniper stands have grown so dense that they have eliminated the native grasses and forbs that once shared their areas. These trees have also spread into — and often overtaken — adjacent sagebrush ranges.

Fires burn much more intensely in these dense, old pinyon-juniper forests. And if there aren't seed reserves of native grasses and forbs in the soil, large swaths of rangelands are susceptible to cheatgrass after a wildfire.

In some areas, Utah's Watershed Restoration Initiative uses physical removal, controlled burns and follow-up seeding work to remove old growth, improve wildlife habitat and prevent the spread of cheatgrass.

Unmanaged grazing damages rangelands.

Although unmanaged livestock grazing can do substantial damage to a watershed, well-managed grazing can improve rangeland health, prevent catastrophic wildfires and enhance habitat for wildlife.

The DWR grazes livestock on some of its own lands and on lands it leases from other organizations. Most grazing occurs in the spring months to enhance shrub growth. In the winter, those same areas provide critical range for mule deer and other wildlife.

Ranchers throughout Utah also depend on healthy rangelands to maintain economically viable livestock operations. Wherever possible, Utah's Watershed Restoration Initiative works closely with state and federal land managers and livestock operators. Together, they implement ecologically sound grazing plans, monitor changes in the plant community and make adjustments when needed to meet management objectives.

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