Factors affecting pronghorn fawn recruitment in central Arizona
Over the past 15 years, pronghorn (Antilopcapra americana) populations appear to have declined in Arizona. Recruitment of fawns into the population rather than adult mortality tends to be the primary determinant of populations in Arizona. The purpose of this study was to examine some factors which may affect differences between pronghorn fawn: doe ratios on the two ranches. Our goal was to determine if nutrition was adequate to support pronghorn and provide favorable conditions for survival and recruitment. This study was part of a statewide evaluation of factors affecting pronghorn fawn recruitment, including predator abundance, nutrition, fawn hiding cover, disease, and water availability throughout pronghorn habitat in Arizona. We studied forage production, and diets of pronghorn during 2003 and 2004 on 2 study sites in central Arizona. Diet composition (microhistological analysis of fecal samples) and selection relative to availability were investigated during gestation and lactation. Forage production during 2003-2004 ranged from 9-304 kg/ha. Forbs made up a major percentage of the biomass in 2003, whereas grasses made up the majority in 2004. Forbs made up 60-69 percent of the diets during gestation and lactation. Grasses were eaten in small quantities during both sampling periods. Browse consumption increased as forbs dried up during lactation. Pronghorn showed selected for forbs and avoided grasses on both study sites. Diet composition was similar on both study sites. Fawn recruitment during our study increased from year 1 to year 2. It appeared that forage conditions during our study were favorable for fawn recruitment.