Occupancy and Detection of an Endemic Habitat Specialist, the Dunes Sagebrush Lizard (Sceloporus arenicolus)

Authors: Danielle K. Walkup, Wade A. Ryberg, Lee A. Fitzgerald, and Toby J. Hibbitts

We estimated occupancy and extinction probabilities for the Dunes Sagebrush Lizard (Sceloporus arenicolus) for part of its range in Texas, to increase our understanding of the distribution of this species and to evaluate the map that identifies areas according to Very High, High, Low, and Very Low categories of likelihood-of-occurrence. This map, developed using expert opinion, has been vital in establishing conservation policies for the species under the Texas Conservation Plan. From May to August 2014–2016, 100 16-ha sites were surveyed by crews of four observers who searched each quadrant of the sites for all lizards. Lizards were identified to species and GPS locations were recorded for Dunes Sagebrush Lizards. Over 336 surveys, 33 Dunes Sagebrush Lizards were detected during 17 surveys at nine sites in areas classified as Very High likelihood of occurrence. Occupancy probability for the Dunes Sagebrush Lizard in the Very High likelihood-of-occurrence areas was 0.32 ± 0.09 (SE), with a detection probability of 0.52 ± 0.12. Local extinction probabilities were low at 0.12 ± 0.18, with the colonization probability fixed at zero. No Dunes Sagebrush Lizards were detected in the 54% of surveys that occurred outside the currently recognized range. Thus, we are confident in the described range boundaries of the Dunes Sagebrush Lizard. The consistent predictability of occurrence of the Dunes Sagebrush Lizard in likelihood-of-occurrence areas rated Very High suggests recovery and conservation actions in areas that have the highest likelihood of occupancy should have highest priority.