State and federal agencies in the western United States have used water developments as an integral component of management of wildlife habitats in arid regions since the 1940’s. Where water was perceived to be limiting, considerable attention was focused by early resource managers on developing water sources for wildlife. Ranchers and range managers have developed water sources for livestock, many of which also are used by wildlife. Indeed, water catchments remain a widely used management tool in the western United States.
Mule deer (Odocoileus hemionus) occupy a variety of habitats throughout western North America and require relatively large areas to assure persistence of viable populations, especially in the Chihuahuan, Sonoran, Mojave, and Great Basin deserts. Mule deer are dependent upon resources, including water and forage, adequate to meet the demands of growth, reproduction, and lactation.
Resources that often are assessed to determine the distribution of desert mule deer are availability of forage, nutritional quality of forage, cover, mating sites, natal sites, and availability of water. In arid regions, mule deer are dependent on free water, and often are located close to sources of water, particularly during dry seasons.
Indeed, physiological demands may dictate that during times of water scarcity, ungulates remain close to water rather than ranging widely to forage. Mule deer in the Sonoran Desert tended to remain close to sources of water during the hot-dry season when water was most scarce, a common occurrence in the southwestern United States. Moreover, water developments in Arizona received heavy use by desert mule deer, primarily during hot summer months. Thus, distribution, abundance, and seasonal availability of water affect the distribution of mule deer across the landscape.
Ungulates use water catchments when they are available; mule deer change distribution and movements relative to catchments and have been observed to use water from catchments as often as 1-2 times per 24 hours during hot-dry weather. Adult females visiting water sources consumed more water than males, likely because of increased water requirements to support lactation. Moreover, females moved outside of their known home ranges to locate alternative sources of water when denied access to catchments.
Developed water sources that have been present for long intervals tend to receive more use than newly developed sources of water. For example, use of washes near water catchments was greatest after catchments had been in place >3 years. Thus, the longer that water sources remain available the more use they receive by mule deer and other species of wildlife.
Sexual segregation outside the mating season is ubiquitous among ungulates, including mule deer. Differences in spatial distributions of sexes of deer hold import for understanding the distribution of these large mammals across the landscape. Bowyer (2004) stated that the concept of sexual segregation must be integrated into the disciplines of range and wildlife management and become a standard consideration in designing research and implementing habitat manipulations.
Sexual segregation has been well documented in mule deer, and differences in spatial distributions between the sexes of mule deer in Mojave Preserve may result in some sources of water being used predominately by a single sex outside the mating season when deer are sexually segregated.
Thus, for the purposes of this study, we must account for the occurrence of sexual segregation or we may under represent the importance of water sites visited predominately by males if, for example, only the female cohort of the population was marked with radio collars. Nevertheless, because mule deer are polygynous, the female cohort of the population has a more direct effect on survival and reproduction; thus we will equip a greater number of females with radio collars than males.
In arid and unpredictable ecosystems, such as those occurring in the eastern Mojave Desert, availability of forage is strongly influenced by climate. Forage availability for mule deer is dependent on plant biomass, which is, in turn, influenced by rainfall. This is particularly true in arid regions where there is a close association between rainfall and plant abundance.
Forage quality also is affected by water available to plants; protein content of forage tended to be lowest during seasons with low rainfall and, consequently, low forage growth. Vegetation surrounding sources of water may access greater quantities of water than vegetation occurring away from water sources, provided there is runoff of water available to the plant community. Thus, vegetation located immediately around water sources may have greater moisture content and higher nutritional quality for mule deer and other wildlife.
Over the past several years, numerous water sources for livestock were deactivated within the Mojave National Preserve. Many of those water sources had been available to native wildlife for periods in excess of 100 years. Deactivation occurred in the absence of any environmental assessment of the potential influences of that action on populations of wildlife, including mule deer, which are widely distributed within the preserve.
The purpose of this investigation is to assess responses of mule deer inhabiting the eastern Mojave Desert to the provision of water at locations where it had been, but is no longer available. Secondarily, we address interactions between mule deer and vegetation as influenced by availability of surface water.
Rosenstock et al. (1999) indicated several areas where research should focus with respect to water developments including:
- effects of water developments on population performance,
- distribution and habitat use of game and non-game wildlife species, and
- secondary effects of water developments on adjacent plant communities.
We propose to test several hypotheses relating to responses of mule deer to provision of water, to evaluate effects of deer use on habitats surrounding those water sources, and availability and quality of forage for mule deer with available water compared with similar areas where water sites had been removed.
The original Environmental Assessment produced by the National Park Service described several additional issues regarding reinstatement of wells in Mojave Preserve. Because addressing each of those issues in this proposal would substantially increase the length we will provide a separate document in which we review the current literature to address those additional concerns. In addition, we will ensure that our water developments will not negatively impact desert tortoise (Gopherus agassizii) in Mojave Preserve, we will not make any water sites unavailable to tortoises and we will make water sites that are turned available and accessible to tortoises.