Horned lizard habitat

Twenty miles south of where Mason Mountain’s horned lizard population had disappeared, a rancher found lizards thriving on his property. Researchers set out to learn why. 

“There’d been kind of this open question [as] to whether the habitat at Mason [Mountain] Wildlife Management Area was suitable,” said Williams. 

Over the summer, graduate biology students Padraic Elliott and Patrick Ryan compared the habitats at the two sites to reveal whether Mason Mountain is a quality environment for horned lizards and how it could be improved.  

Elliott studies plants, so when the Williams lab needed a student to research the vegetation at the two areas, “I jumped at that opportunity,” he said. 

By examining the size, species and diversity of plants at Mason Mountain and the ranch site, his project adds “one more tool” to finding the secret sauce for successful reintroductions. 

Ryan, who often collected data alongside Elliott, focused on the thermal habitat of the lizards. 

Since lizards are ectotherms, or cold-blooded animals, they cannot regulate their body temperature to cool off and can die if temperatures rise above their “critical limit” of about 40 degrees Celsius, or 104 degrees Fahrenheit. 

Ryan placed devices that record temperature in different “microhabitats” lizards use - dense vegetation, open areas and soil - at the ranch and Mason Mountain.

If the thermal habitats at the two sites are significantly different, “Kind of the assumption is that that natural population is the better habitat because it’s been sustaining this natural population, where at these reintroduction sites they can’t get a foothold there,” said Ryan. 

^{Photo: A tagged Texas horned lizard rests near vegetation. (Photo courtesy Dean Williams)}

To study the lizards, the students have to find them first. 

Adult lizards were caught and fitted with radio transmitters that broadcast a unique frequency for each lizard up to a kilometer away.

The frequencies are picked up as “beeps” by handheld receivers with antennas that help students determine the direction of the transmitter. The louder the sound, the closer the lizard.

“It’s like playing hot and cold,” said Ryan. 

Hatchlings were too small for the radio transmitters, so researchers opted for another tracking device called harmonic radar. The team glued reflective tags attached to a strip resembling 35-millimeter film to the back of the lizards. 

Rains said the harmonic tags were useful but had drawbacks for tracking the lizards. 

“Like any reptile, they shed their outer skin off, so there’s a limited time we can track them,” he said. 

The students attempted to find every tagged horned lizard once a day. Even with the tags, spotting them could be a challenge. If the tag had fallen off, the lizards were almost impossible to find. 

Every day or two, the students would change the time they tracked an individual to make sure their data reflected the lizards’ daily patterns. 

“We were working probably about nine, 10-hour days to make sure that our data was not biased or was taking into account the time of day,” said Elliott. 

In addition to collecting data for their own projects, they also gathered information on the size, sex and age of the lizards and logged deaths from predators. It may sound simplistic, but it’s some of the first data of its kind. 

“Because we’re dealing with reintroduction animals for our project, those haven’t been looked at before in this level of detail,” said Ryan. 

Rains said the students’ role in tracking the lizards is one of the most important parts of the reintroduction project. 

“That’s really the only way we can evaluate what’s happening to them,” said Rains. 

^{Photo: A Texas horned lizard hatchling seems to "smile" for the camera. (Photo courtesy Padraic Elliott)}