Abstract - Factors Influencing a Declining Pronghorn Populations in Wind Cave National Park, South Dakota
Sievers, Jaret D. 2004. Factors Influencing a Declining Pronghorn Populations in Wind Cave National Park, South Dakota. Thesis submitted in partial fulfillment of the requirements for the MS degree, South Dakota State University. 92 p.
Pronghorn (Antilocapra americana) were reintroducted into Wind Cave National Park (WCNP) in 1914 and thus, have inhabited the park for almost a century. A decline in the populations has raised concern for the continued existence of pronghorn inside the park. Historically, pronghorn numbers reached greater than 300 individuals but were estimated to be less than 50 individuals during this study. Knowledge of food habits, genetic structure, causes of mortality, survival rates and information related to movements were important to developing an understanding of factors contributing to this decline. Past studies have described spatial relationships and breeding behavior of adults and survival strategies of neonates. However, direct information was not available on the recent decline of pronghorn in WCNP. The primary objectives of this study were to identify factors contributing to the decline of pronghorn in WCNP with regard to movements, mortality (e.g., predation), diet quality, and genetic variation. A secondary objective was to identify characteristics of daytime bed sites used by pronghorn neonates during the first three weeks of life. Radio telemetry was used to monitor the movements and mortality of 8 adult (> 1 year at capture) and 19 neonate (< 1 month at capture) pronghorn from 26 January 2002 to 31 May 2004. During the study, visual locations were obtained on 8 adult females (n=407), 3 adult males (n=177), and 19 neonates (n=148). Mean daily distance traveled by radiocollared females was 2.6 km (n=8) in winter and 2.5 km (n=8) in summer. Ninety-five percent home range contours calculated for radiocollared females were 66.6 km² (n=8) during winter and 54.5 km² (n=8) during summer. Fifty percent core use contours were 7.2 km² (n=8) during winter and 7.3 km² (n=8) during summer. The longest summer movement of a radiocollared adult female was 11.5 km, and the longest winter movement was 11.0 km. Survival of adult female pronghorn was 87.5% in 2002 and 85.7% in 2003. Predation accounted for all adult pronghorn deaths during the study. Survival of pronghorn neonates was 22.2% in 2002 and 41.7% in 2003. Coyotes (Canis latrans) accounted for 50% of fawn deaths and likely contributed to mortalities of neonates from unknown predators. Fifty daytime fawn bed sites and 50 random sites was not significantly different from random sites in 2002 (P=0.959). However, significant differences were observed in height of vegetation between bed sites and random sites in 2003 (P=0.059). Microhistological fecal analysis was conducted on 58 samples collected from pronghorn in 2002. Blue grama (Bouteloua gracilis), common juniper (Juniperus communis), and northern bedstraw (Galium boreale) were identified as important seasonal food items, representing 14.6, 10.6, and 6.5% of the annual diet, respectively. Annual diets of pronghorn in WCNP included 41.5% grasses, 31.1% shrubs, and 27.4% fords. Microsatellite DNA collected from 75 pronghorn in WCNP (n=11), Harding County (n=33), and Fall River County (n=31), South Dakota, showed similar levels of observed heterozygosity (0.473 to 0.594) and low inbreeding coefficients (-0.168 to 0.037). These results indicated that fawn mortality and availability of forage were significant factors limiting population growth in pronghorn within WCNP during this study.