Accuracy of two techniques used to estimate pronghorn (Antilocapra americana) numbers in Chihuahuan Desert rangelands

Abstract

Two techniques frequently used for monitoring pronghorn populations were compared in vegetation communities of the Chihuahuan Desert in New Mexico, USA. The evaluated techniques included the walking line transect and the driving line transect under two vegetation types and relative to season. The true population value (control) used to evaluate the techniques was a complete census using flights conducted over the entire study area (8000 ha). On grassland vegetation, the walking transect overestimates pronghorn density (n/km2), compared with the control (0.77 vs. 0.18 n/km2), as well as in the mesquite-grassland vegetation where the walking transect overestimates density (0.26 n/km2) compared with the control (0.11 n/km2). An increase in overestimation was found in the walking technique as the number of pronghorns in an area increased. In contrast, the driving technique showed no significant differences (P>0.05) compared with the control, in both grassland and mesquite-grassland pastures. It can be concluded that driving transect sampling is an accurate method to study pronghorn densities in the Chihuahuan Desert ecosystem, while walking transect sampling estimations need to be adjusted to obtain accurate population sizes. © 2013 Copyright Taylor and Francis Group, LLC.