No abstract

We documented adult mortality and fawn recruitment of Sonoran pronghorn (Antilocapra americana sonoriensis) in Arizona. This population is endangered (N < 30) and is decreasing due to low fawn recruitment and adult mortality. We radiocollared Sonoran pronghorn to monitor survival and recruitment from 1995–2002. We relocated each radiocollared pronghorn during weekly telemetry flights from a fixed‐wing airplane and recorded group composition to determine recruitment. Mortalities detected during flights were investigated as soon as possible (i.e., < 48 hours) to document adult mortality. Adult mortality rates varied from 11–83%/year. Adult pronghorn were killed by coyotes (Canis latrans), bobcats (Felis rufus), mountain lions (Puma concolor), capturing efforts, drought, and unknown causes. Fawn mortality varied from year to year and was correlated with the amount and timing of rainfall. Drought may be a major factor in the survival of adults and fawns. A lack of nutritious forage and water, caused by dry conditions, led to high fawn mortality and caused adult mortality during a particularly severe drought. Drought also may indirectly affect adult mortality by causing animals to use areas where predators are more successful. Disease may affect mortality but remains largely uninvestigated. Management applications aimed at increasing fawn recruitment and reducing adult mortality should increase the chances of survival of this species. Providing sources of highly nutritious forage during early spring and summer when fawns are susceptible to poor nutrition may increase their chances of survival. Providing water sources and nutritious forage in areas where predators are less successful may increase both adult and fawn survival. Predator control may be useful in limited situations but likely would be prohibitively expensive, with little chance of making a difference over the entire range of Sonoran pronghorn.

The Sonoran pronghorn (Antilocapra americana sonoriensis) is one of the most endangered ungulates in North America. The use of water to improve its habitat in southwestern Arizona has been limited in part because published reports claimed these desert ungulates do not use freestanding water. Because free‐standing water has been beneficial to habitat improvement of other desert ungulates, we set up cameras at anthropogenic waters to see if they were used by pronghorn, examined literature and agency files related to Sonoran pronghorn and water, and interviewed ranchers who have lived and managed livestock in Sonoran pronghorn habitat since the 1930s regarding their observations of pronghorn use of livestock waters. Using direct observation and photographic evidence, we documented Sonoran pronghorn drinking freestanding water. Published reports claiming that Sonoran pronghorn do not drink were erroneous. Ranchers, agency files, and biologists from numerous state and federal agencies documented Sonoran pronghorn drinking. Federal and state agencies should be aggressive in examining how water developments can be used to assist in recovery of endangered Sonoran pronghorn.

A population of endangered Sonoran pronghorn (Antilocapra americana sonoriensis) exists in the United States, and 2 populations exist in Mexico. Because of the vulnerability of small, remnant populations of this subspecies to stochastic events, an important aspect of recovery planning is identifying suitable areas for establishment of new populations. To support translocation efforts, we developed landscape‐level Classification and Regression Tree (CART) and logistic regression models of potential Sonoran pronghorn habitat in southwestern Arizona through a 2‐part modeling process. First, we used approximately half of Sonoran pronghorn locations (total n=3,219, collected from 1994 to 2002 from radiocollared animals in the United States) and unused points (total n=3,142, randomly generated in areas within the range of Sonoran pronghorn below 21% slope, but >1.6 km from pronghorn locations) to create habitat models from 5 explanatory variables (i.e., slope, aspect, biome, distance to wash, and soil category). We validated models with the second half of pronghorn and unused points. Both models determined whether areas would or would not be used by Sonoran pronghorn based upon values of explanatory variables at Sonoran pronghorn locations and unused points. The CART model correctly identified 63% of pronghorn locations and 65% of unused points. The logistic regression model correctly identified 57% of pronghorn locations and 62% of unused points. Second, we created a predictive Geographic Information System (GIS) map of Sonoran pronghorn habitat and applied it to the evaluation area. Both models identified >12,000 km2 of potential habitat for Sonoran pronghorn on the evaluation area. Our models are a first step toward identifying potential translocation sites for Sonoran pronghorn. Potential translocation sites should be further evaluated with respect to habitat factors not included in our models, including barriers to pronghorn movements, water supplies, and forage resources.

We studied the diets of desert mule deer (Odbcoileus hemionus crooki Mearns) at 3 sites in Arizona and collated this information with that of previous diet studies of desert mule deer across their range in the United States. We documented 96 browse, 69 forb, 14 succulent, and 6 grass species that each constituted 2 1% of the diet during 2 1 season. The occurrence of individual plant species varied spatially and temporally. Changes in nutrient levels and climatic influence on relative availability and phenology of plant species likely influenced diet. Desert mule deer rely heavily on browse and forbes, which make up the majority of their diet (> 90%). Grasses and succulents were generally c 5% of the diet. Rangeland managers should strive to keep desert rangelands productive with a diversity of forage so animals have opportunities to exercise free choice of diet.