ESTIMATION OF SWIFT FOX POPULATION SIZE AND OCCUPANCY RATES IN EASTERN COLORADO

Abstract

Abstract The status of the swift fox (Vulpes velox) became a subject of controversy when a petition was submitted in 1992 to have it listed under the provisions of the Endangered Species Act. Colorado is believed to have one of the largest remaining populations of the species due to significant amounts of short-grass prairie habitat suitable for occupancy. In 1995, we initiated a survey in eastern Colorado to determine swift fox population size and presence or absence on 724.8×6.4 km2 grids trapped with 20 live traps. We drew trapping grids from a stratified random sample of grids plotted on 1:100,000 scale Gap vegetation maps of eastern Colorado. Of the grids sampled, 54% were from areas with 75% short-grass habitat. We captured 241 swift foxes (117 male, 121 female, and 3 undetermined) on 51 (71%) of the grids. We estimated a mean capture probability per night of an individual fox, weighted by number of grids and number of trapping occasions for each grid, as 0.234 (SE = 0.022). Highest capture and dete...