Outdoor News Bulletin
American Pronghorn Movements in the Chihuahuan Desert, New Mexico
USGS researchers at the New Mexico Cooperative Fish and Wildlife Research Unit are leading efforts to monitor American pronghorn (hereafter, pronghorn) movements in the Chihuahuan desert grasslands in southwestern New Mexico. The goals of this 3-year project are to monitor space use and movements, identify barriers to movement, and assess habitat use patterns, particularly in relation to vegetation restoration treatments by the Bureau of Land Management (BLM). Vegetation restoration treatments involve strategies to enhance and restore healthy ecosystems, specifically in areas affected by wildfires, invasive species, human activity, and environmental degradation.
Large Mammal Movements
The landscapes that large mammals need to move freely are becoming increasingly fragmented. This can make it harder for migratory mammals, like mule deer and pronghorn, to cope with changes in habitat and food availability caused by human activities and weather.
Migratory mammals rely on separate seasonal ranges (areas where these animals live at different times of the year), making the management of migration routes critical for conservation. Conserving movement corridors that allow migratory ungulates to exploit phenological gradients in forage growth is well documented.
Secretarial Order 3362
Funding provided to state and federal agencies from Secretarial Order 3362 (Improving Habitat Quality in Western Big Game Winter Range and Migration Corridors) has contributed to substantial efforts to identify, map and monitor big game migration routes across the western U.S.
Functional habitats are also vital for non-migratory ungulates with resident or nomadic movement strategies. Regardless of their movement strategies, large mammal populations require landscapes with sufficient forage resources to maintain their population health and ensure long-term survival. Additionally, landscapes must be navigable to allow these animals to efficiently access changing food sources over time.
Non-migratory populations characterize most mule deer and pronghorn populations across the lower elevation and more arid portions of the southwestern U.S. Mapping efforts for these populations are not covered by funding from Secretarial Order 3362, resulting in a gap in the knowledge of animal movements needed to make informed land management decisions. Adaptive movements by non-migratory populations allow animals to efficiently exploit changes in forage conditions. These movements are critical for ungulate populations, as they allow them to maximize nutritional gain, enhance survival and recruitment, and increase probability of population persistence.
"The research done by Lucas Begeman and Dr. Cain will be integral to restoration efforts for pronghorn in the Las Cruces District Office. Their hard work will allow us to efficiently address barriers on the landscape and confidently improve habitat for this species." Cody Howard, Wildlife Biologist, Bureau of Land Management
Pronghorn require high quality diets comprised mainly of forbs and grasses. Pronghorn populations are sensitive to changes in precipitation and forage conditions, particularly on their arid and semi-arid ranges in the Southwest. For example, pronghorn fawn recruitment and adult survival in west Texas were associated with short and long-term precipitation, respectively. Evaluation of the relationship between temperature, rainfall and population growth rate for 18 pronghorn populations across Arizona, New Mexico, Texas, and Utah found links between population growth and precipitation for 16 populations.
Chihuahuan Desert Weather
Pronghorn population performance in the Southwest is strongly linked with rainfall. Recurring drought conditions in the short term will likely contribute to reduced forage quality and quantity impacting survival of adults and fawns and long-term declines in rainfall may decrease the likelihood of population persistence. Forage dynamics in the Chihuahuan Desert are primarily dependent on summer monsoon rains. The highly variable distribution of monsoon rainfall during summer frequently leads to high spatial and temporal variation in the availability and nutritional quality of forage, requiring greater search times and travel distances. Therefore, pronghorn in Southwestern deserts depend on highly connected landscapes with low movement costs to take full advantage of this dynamic nutritional landscape.
Barriers to Animal Movement - Fences
Across the western U.S., impediments to wildlife movements proliferated with the spread of humans following the Homestead Act of 1862 which led to the rise of barbed wire fencing used to mark property boundaries and control livestock movements. The lease of state and federal lands for grazing and production of livestock is widespread and public lands are often partitioned into grazing allotments, with allotment boundaries and internal pastures defined by fences.
Today, approximately 155 million acres of BLM and 74 million acres of U.S. Forest Service lands are managed as active grazing allotments. Fences can decrease how easily some wildlife move through their environment. The degree of movement across barriers, like fences, depends on the specific design of the fence, the terrain and the abilities of different species to get over or under the fence.
Pronghorn movements can be restricted by fences due to their behavioral unwillingness to jump over obstacles. Pronghorn typically crawl through or under barbed-wire fences. This can result in injury from barbed wire, direct mortality from becoming entangled, or altered movement patterns when they are unable to cross. Barbed wire fences can be modified, making them less of a barrier to pronghorn movement. Given the number of fences across pronghorn ranges in the Southwest, coupled with limited resources for fence modifications, data on altered pronghorn movements with respect to fences can be helpful for guiding fence modification efforts.
Delivering Actionable and Applied Science for Fish and Wildlife Management to Cooperating Agencies and Organizations
The analysis of pronghorn movements may provide the BLM and New Mexico Department of Game and Fish with information on how this population is utilizing the landscape and interacting with rangeland infrastructure, including fences. By quantifying how individual barriers on the landscape may be influencing pronghorn movements across the landscape, researchers hope to identify specific barriers or corridors where modifications to barriers can increase animal movements across the landscape, reducing habitat fragmentation and improving access to available forage. A better understanding of the effects of infrastructure and other human features have on pronghorn movements is crucial to conservation and management.
The ONB features articles from Cooperative Fish and Wildlife Research Units across the country. We believe our readers will appreciate discovering stories about the exciting fish and wildlife research projects that Unit scientists are conducting to solve real-world problems, engage graduate students in experiential learning, and deliver technical assistance to natural resource practitioners. This story is authored by James Cain, jwcain@nmsu.edu, USGS scientist and Unit Leader at the New Mexico Cooperative Fish and Wildlife Research Unit and Lucas Begeman, lbegeman@nmsu.edu, Master’s Student, Department of Fish, Wildlife and Conservation Ecology at New Mexico State University. Story edited by Dawn Childs, dchilds@usgs.gov, USGS Information Specialist, Cooperative Fish and Wildlife Research Units
