Survivorship and Spatial Ecology of Texas Horned Lizards at Tinker Air Force Base

Abstract

Habitat fragmentation has negative consequences on threatened and endangered species by creating isolated populations within urban settings. The Texas horned lizard (Phrynosoma cornutum) is experiencing population declines and localized extirpations throughout its range and is now considered a species of greatest conservation need in Oklahoma, USA. While adults of this species have been extensively studied, subadults remain understudied, yet may be vital to the stability of remaining populations. To address the gaps in knowledge, we used a combination of traditional radio telemetry and novel harmonic radar methodology to assess the survivorship and movement of two cohorts of subadult Texas horned lizards within a closed population at Tinker Air Force Base, a large military installation in central Oklahoma. Each cohort was monitored across a two-year period, resulting in a study that spanned four years in total (2016–2019). We provide the first robust, baseline estimate of wild-born hatchling survivorship in this species. Our lowest estimates of survival indicate an average survival probability for the hatchling life stage (0.285; 95% CI 0.15–0.44), within the range or slightly higher than previously predicted for the population. Average home range size was calculated with 95% minimum convex polygons, with results supporting ontogenetic increases in home range area required for Texas horned lizards from hatchling to adult life stages. We also provide age-class specific morphometric averages and updated population abundance and density estimates for this small, urban population. Our results inform the planning and assessment of future headstart and management programs for Texas horned lizards.