Evaluation of Methods Used to Estimate Size of a Population of Desert Bighorn Sheep (Ovis canadensis mexicana) in New Mexico

Abstract

Reliable estimates of size of populations are critical for successful management of translocated desert bighorn sheep (Ovis canadensis mexicana). As costs decrease and quality improves, remote cameras are increasingly used as a non-invasive tool to monitor populations of wildlife, but their efficacy has yet to be evaluated in a diversity of species and habitats. Here we investigate whether remote cameras, in combination with a simple mark-resight model, produce estimates of size of populations of desert bighorn sheep comparable to those derived from surveys conducted on the ground and using helicopters in the Fra Cristobal Range of south-central New Mexico. We determined that estimates of size of populations derived from remote cameras were comparable to those produced from direct observations obtained by surveys from helicopters and on the ground, that ca. 25 sequential samples of photographs produced comparable estimates of size of populations, but that photographs of single desert bighorn sheep dramatically lowered estimates of size of populations, and that placement of remote cameras on wildlife guzzlers in July produced the greatest number of photographs in the shortest time. Our results suggest that use of remote cameras may be an accurate, low-cost, and non-invasive means of estimating size of populations of desert bighorn sheep in New Mexico. Further research is warranted, ideally in tandem with ongoing surveys on the ground and using helicopters, in other management areas.