programs Natural Resources

Spot-tailed Earless Lizard

(Holbrookia lacerata)

Background

The spot-tailed earless lizard (STEL) is notable for a row of black spots on the underside of its tail, for a lack of external ear openings and for confusing generations of Texas herpetologists.

The five-inch-long lizard historically occupied sparsely vegetated habitats across 50 counties in West, Central and South Texas. Anecdotal evidence suggests the species has experienced an overall population decline. Potential causes of few sightings and suspected extirpations include native grassland loss, use of pesticides and the spread of invasive fire ants. The U.S. Fish and Wildlife Service (FWS) is expected to make a listing proposal by 2022.

The FWS decision to consider listing the species under the Endangered Species Act kick-started a lizard research campaign on a scale never seen before. Researchers from state agencies, universities and nonprofit organizations began field surveys using both traditional and new methods. They scrutinized museum collections across the country to find every possible STEL record and compare physical and genetic differences across populations. The focus was on establishing the distribution, population size and basic life history traits of the species.

Research Description

The Texas Comptroller of Public Accounts (CPA) contracted with the University of Texas at Austin (UT) in 2014 to supply life history information for the spot-tailed earless lizard to inform the FWS’ species status assessment and educate stakeholders, who ranged from farmers on the coast to oil and gas developers in the Permian Basin.

UT researchers set out to collect data pertinent to identifying the species’ needs and current condition. Field surveys have been ongoing since 2014 and have increased the understanding of the lizard’s distribution, genetics, habitat suitability and land use. In 2017 the CPA began a second contract with UT to focus on home range size, movement patterns and habitat usage and provide insight into how individuals interact with other spot-tailed earless lizards and their environment. Researchers capture and fit adult lizards with radio transmitters to track their daily movements with minimal disturbance. Researchers may further advance the study of individual movement, dispersal and habitat use by using lightweight harmonic radar tags that are small enough for juveniles.

Additional studies funded by the new research contract include lizard responses to land use practices (e.g., grazing, farming, prescribed burning and renewable energy or oil and gas development) and food availability. The study of lizard diet and prey availability may offer insight into the potential threat of pesticides indicated in the listing petition. Stomach contents of museum-vouchered lizards suggest that spot-tailed earless lizards dine on an assortment of insects with a slight preference for grasshoppers. Ongoing lizard surveys incorporate insect collections in known and unknown STEL habitat to compare potential relationships between trends in insect availability, land use and lizard abundance.

Deliverables Due at Contract End, Oct. 31, 2019

  • Report and analysis regarding:
    • Activity periods, home range, movement and habitat use of the spot-tailed earless lizard and its response to various landscape disturbances
    • Threats to and viability of the species
  • Supporting data and documentation including raw data, maps, photos and field notes

Why This Research Matters

Recent discussions of the status of spot-tailed earless lizards have highlighted the lack of understanding about the basic life history and potential threats to the species. This fundamental information is needed to evaluate the lizard’s status, identify potential threats and ensure the effectiveness of conservation actions. In turn, this information will be useful for providing regulatory certainty for agriculture, urban development and energy exploration and production throughout West and South Texas.