Model Construction:
We constructed horned lizard models and controls using urethane foam, a
material that has proven effective at withstanding Texas summertime
temperatures in excess of 38°C and preserving marks left behind by
predation (Farallo and Forstner 2012). We constructed molds using Mold
Max 29NV® silicone rubber (Smooth-On) and a pewter replica of an adult
Texas horned lizard (84 mm snout-to-vent length, SVL). The original
pewter horned lizard replica was scanned to create an object file (.obj)
that was used to 3D print three size classes of model Texas horned
lizards: hatchling (23 mm SVL), juvenile (50 mm SVL), and adult (84 mm
SVL) size models. We used these 3D printed models to create molds
capable of producing the different size classes used in this study and
multiple models per casting. Foam iT! 3® urethane foam (Smooth-On) was
poured into the molds and allowed to cure for 2 hours. The controls were
constructed from round pieces of urethane foam left over from casting
the lizard models and painted with acrylic paint and otherwise treated
exactly like the lizard models to control for predators being attracted
to the foam material or to the paint (Fig. 1).
We painted models and control pieces using acrylic paint to match two
distinct color variations of Texas horned lizards (Fig. 1); gray lizards
from the urban environments of Kenedy and Karnes City where the
substrate is varied but predominately gray in color, and red colored
lizards from a population found in the natural ranch setting in Dimmit
County where the substrate is characterized largely by red soils. The
specific colors of the models were determined using photographs of
multiple adult Texas horned lizards from each location where models were
placed, as well as from photographs taken of the surrounding substrates.
The PANTONE Studio app (X-Rite) for iPhone was used to take photos of
the substrates where lizards were previously found to select colors for
the models that would accurately resemble local lizards, as well as,
background color-match the substrates. After painting, we placed dried
models outside and covered them with a loose layer of soil to allow
paint fumes to dissipate for a period of 7 days prior to placing them in
the field.