Texas horned lizards (Phrynosoma cornutum) have been declining in abundance and experiencing a westward range contraction since the 1960s and possibly earlier. They were once relatively common throughout Texas except for the dense pine forests in the easternmost part of the state. Their current geographic range extends in latitude from Kansas south into Mexico and in longitude from west-central Texas to Arizona (see P_cornutum_IUCN). There are also small introduced populations in Florida and South Carolina. The decline and range contraction is likely due to multiple causes including habitat loss, decline in harvester ants (main food resource), increased use of pesticides, and predation by feral cats. Further the range contraction might not be completely anthropogenic; natural long-term trends in precipitation and subsequent effects on vegetation (habitat) and the prey base may be partly responsible. Regardless, the Texas horned lizard and possibly other Phrynosoma species (there are 17, all in North America) likely need attention toward their conservation.

As a kid growing up in Brazos County, Texas, I often found horned lizards in natural areas near my neighborhood. However, by the mid-1980s they had disappeared. While in graduate school in Nevada, I often saw them (a different species than P. cornutum) at some of my study sites while conducting research on rodent-plant interactions. Prior to moving back to Texas in 2008, I lived in Colorado and did some field research out on the plains where P. hernandesi was very common. …. So, horned lizards have been on my mind (off and on) for a while. A few years ago I decided to initiate some research projects on Texas horned lizards.

The first project was intended to design and test out a road-cruising method for surveying the lizards, combined with the use of N-mixture models to estimate detection probability and abundance. Horned lizards can be very cryptic against a natural substrate and they often freeze when approached by a human or predator – this can make it very difficult to detect them when surveying such as walking line transects through their natural habitat. This project was conducted by graduate student, Tempest Cave, at the Chaparral Wildlife Management Area in south Texas, west of Cotulla. This site was ideal because it had a healthy population of horned lizards and tens of km of narrow one-lane paved roads (closed to the public) for us to drive while surveying. The lizards readily come out onto the road in the morning and late afternoon to bask. So, the survey consisted of driving at slow speeds and visually looking for lizards in the road. We also collected ancillary data to use in the N-mixture models. The project turned out pretty well and Tempest is writing it up for her thesis.

The second project was a very comprehensive study of the survival, movement (dispersal), and habitat selection of horned lizards released at a reintroduction site (Mason Mountain Wildlife Management Area in north-central Texas north of Fredericksburg). Using radio-telemetry, graduate student Alyssa Fink, tracked the survival and daily movement of over 20 horned lizards throughout Summer 2016. Most of the lizards were surprisingly sedentary, typically not venturing more than 50 m from their release enclosure. There was some initial mortality in the first week or so, after which survival was fairly high from week to week. The lizards tended to use microhabitats (shrub, grass clump, bare ground) in about the same proportion as background availability. There was not a strong preference for a particular microhabitat. It is likely that the use of a mix of microhabitats allows the lizards to efficiently thermoregulate throughout the day.

I am planning to continue ecological studies and conservation work on Texas horned lizards and perhaps other Phrynosoma species. I am interested in advising grad students working on additional horned lizard projects. My newest grad student, Jared Haney, is developing a project to better analyze and document the spatial pattern of range contraction in P. cornutum.