Evaluation of aerial line transect for estimating pronghorn antelope abundance in low-density populations

Abstract

Recent trend surveys have indicated that pronghorn antelope (Antilocapra americana) populations have declined in Oregon. However, fluctuations of up to 50% from year to year suggest that trend data may not accurately reflect true population changes, and data reliability may be questioned if proposals for mitigating population declines become contentious. We evaluated aerial line transect iLT) lor estimating pronghorn antelope abundance in Oregon. We conducted surveys in 2 Oregon Big Game Management Units (BGU) during May 1998 and 1 BGU during May 1999 and 2000. We found LT sampling provided reasonable estimates of population size in our survey areas where densities were lower that in other states already utilizing the technique. However, 95% confidence intervals for estimates were large. In addition, application to low-density populations was more expensive compared to traditional survey methods because additional effort was required to obtain desired sample size and resulting precision. Relative comparisons with historic trend counts and management implications are discussed.