Seasonal Movements and Home-Range Use by Female Pronghorns in Sagebrush-Steppe Communities of Western South Dakota

Abstract

Knowledge of seasonal movements by pronghorns (Antilocapra americana) within the easternmost extension of sagebrush-steppe communities is limited. Current hypotheses regarding movement patterns suggest that pronghorns initiate seasonal movements in response to severe winter weather, snowfall patterns, spatial and temporal variation in forage abundance, and availability of water. From January 2002 to August 2005, we monitored movements of 76 adult (� 1.5 years) female pronghorns on 2 study areas (Harding and Fall River counties) in western South Dakota. We collected 8,750 visual locations, calculated 204 home ranges, and documented 17 seasonal movements. Eighty-four percent (n ¼ 55) of pronghorns were nonmigratory and 10% (n ¼ 6) were conditional migrators. Mean distance between summer and winter range was 23.1 km (SE ¼ 2.8 km, n ¼ 13). Five adult pronghorns (8%) dispersed a mean distance of 37.6 km (SE ¼ 12.4 km); of which 1 female moved a straight-line distance of 75.0 km. Winter and summer home-range size varied (P , 0.0001) between study sites. Mean 95% adaptive kernel winter and summer home-range size of pronghorns was 55.5 and 19.7 km 2 , respectively, in Harding County and 127.2 and 65.9 km 2 , respectively, in Fall River County. Nonmigratory behavior exhibited by pronghorns was likely associated with minimal snow cover and moderate temperatures during winter 2002–2004. Variation in size of adult seasonal home ranges between sites was likely associated with differences in forage distribution and availability between regions.