programs Natural Resources

Spot-tailed Earless Lizards Detection

(Holbrookia lacerata and Holbrookia subcaudalis)


A juvenile plateau spot-tailed earless lizard remains motionless to avoid detection near Junction, Texas. 2018 June. Photo credit: Colin McDonald

Historically occupying 50 counties across West, Central and South Texas, two species of spot-tailed earless lizards (STEL), Holbrookia lacerata and Holbrookia subcaudalis, are so elusive that surveying for them is often compared to searching for a needle in a haystack. When startled, these lizards sprint to the nearest crevice or thick vegetation and evade researchers, resource managers and curious landowners seeking to understand them.

Research funded by the Comptroller’s Natural Resources Program has made tremendous strides toward improving our understanding of both species. However, new research questions are frequently hamstrung by the inability to reliably detect the lizards. Low detection rates could reflect low lizard abundance or may indicate that the optimal survey method for them is yet to be discovered. New research is geared toward determining which survey tool is best suited for STEL detection.

Research Description

In 2021, the Natural Resources Program partnered with the Caesar Kleberg Wildlife Research Institute at Texas A&M University–Kingsville to inform the development of best practices to efficiently and effectively survey for STEL.

To meet this goal, the research team will run a series of controlled experiments designed to test survey techniques on a captive population of lizards. Experiments will enable the team to compare eight survey techniques, ranging from pitfall traps to specially trained detection dogs, on a known number of lizards. In addition, the research team will test methods to chemically detect STEL. The team will collect and analyze soil samples for traces of the lizards typically left by shed skin cells and excrement. This is known as environmental DNA (eDNA).

Detailed habitat assessments and imagery collection will help researchers pinpoint ideal conditions to locate STEL. This information will support field surveys where the team tests the most effective experimental techniques across a variety of habitat types. Lizard and habitat data collected throughout the field season will contribute to the development of a population viability analysis to inform the long-term conservation of STEL.

The research team will coordinate with stakeholders to evaluate the cost and feasibility of applying standardized survey techniques to find STEL. The outcomes of this research will improve survey efficacy to facilitate future research and monitoring for STEL and their habitats.

Deliverables Due at Contract End, June 30, 2023

  • Report and analysis of study results to determine:
    • Most efficient methods of identifying presence, relative abundance and probability of detection of STEL
    • Efficacy of eDNA collection to detect STEL
  • Data from all bimonthly field surveys for spot-tailed earless lizards including:
    • Individual STEL data, such as location, size and diet samples
    • Encounters of all other species to inform STEL community and habitat associations
    • Very high-resolution imagery and environmental data

Why this work matters

The U.S. Fish and Wildlife Service is evaluating STEL for listing under the Endangered Species Act in 2022. This work seeks to provide tools to reliably detect lizards for ongoing conservation. In addition, more efficient survey tools may open new opportunities to address questions about STEL and add insight into Texas grassland habitat health.