Photo by Jos Pez O

Analysis of Kit Fox Occupancy in the Trans-Pecos, Texas

Matthew O. Hewitt, Dana Karelus, Patricia Moody Harveson, Louis A. Harveson, and Russell Martin (TPWD)

Management of a species requires knowledge of their distribution and the environmental features that influence their use of an area. The kit fox (Vulpes macrotis) is a small fox species endemic to the threatened desert grasslands of the western United States and northern Mexico. Detailed distribution information on their range in Texas was lacking, but the state had documented population declines in the closely related swift fox (Vuples velox). Therefore, our objectives were to investigate kit fox occupancy, and the environmental features influencing their distribution, across their broad suspected range in the Trans-Pecos (7,135 square miles), and create a predictive occupancy map for the region.

We conducted camera trap surveys at 772 baited sites from March 2018 to March 2020, with each survey lasting 14 days on average (11,205 trap-days). We captured 339 one-hour independent kit fox photos at 105 camera survey sites. We divided surveys into 3-day sampling occasions and fit single season occupancy models and tested for an effect of sampling occasion on detection and for additive effects of slope, elevation, shrub height, and shrub cover on occupancy.

Overall detection ± standard error was 0.46 ± 0.04 and was influenced by sampling occasion, whereby detection was highest on the first occasion and decreased afterwards. Average overall occupancy for surveys was 0.16 ± 0.01 (range: 0.00–0.82) and was influenced by all four environmental covariates, with greatest occupancy where there were shallower slopes, lower elevations, and shorter shrubs covering less of the area. We used the model to make a predictive map of occupancy across the Trans-Pecos region and overlaid kit fox sightings from other sources.

Funding source: Texas Parks and Wildlife Department.