Cooperative Fish and Wildlife Research Units Program: New Mexico
Education, Research and Technical Assistance for Managing Our Natural Resources

A population of pronghorn on White Sands Missile Range (WSMR), in south-central New Mexico, has declined since 1980. While this decreasing trend has coincided with intermittent periods of severe drought, competition with the non-native South African gemsbok is presumed as a contributor to the overall decline of the population. Thus the goal of this study was to relate seasonal changes in forage quality throughout pronghorn habitat on WSMR and relate these seasonal changes to diet composition and nutrition and evaluate dietary overlap between pronghorn and gemsbok. Dietary quality (fecal nitrogen, FN and fecal 2,6-diamonphelic acid, FDAPA) reflected seasonal differences in available forage as well as severe drought. Average FN increased in pronghorn from 1.4% in the cool-dry season (2010) to 2.1% in the warm-dry (2010) season. In contrast, FN decreased in pronghorn from 2.1% in the warm-dry (2010) to 1.4% in the drought of the warm-dry season (2011). Diet composition revealed pronghorn consumed 75 species with forbs representing the major component in the diet (42-68%) in contrast to grasses (2-21%). Although gemsbok and pronghorn share the same habitat (were often seen grazing together), an analysis of dietary overlap between the two species revealed low (17%) to moderate (37%) overlap and suggests the gemsbok are not negatively influencing forage selection of pronghorn on WSMR. Gemsbok dietary quality did not differ between warm-dry (2010) and the drought of the warm-dry season of 2011, revealing resiliency in the gemsbok compared to the pronghorn during abnormally low precipitation periods.