Field Sites:
We placed models in three locations: Kenedy and Karnes City in Karnes
County, Texas served as urban environments, whereas a private 1,200-ha
hunting ranch in Dimmit County, Texas served as a natural habitat.
Karnes City and Kenedy are two small towns (3,299 – 3,337 people) known
for having Texas horned lizards, and are the sites of ongoing studies.
We have censused 15-17 study plots in Kenedy (3 – 4 study plots) and
Karnes City (12 - 13 study plots) since 2013 (Wall 2014, Ackel 2015,
Alenius 2018). The study plots are irregular in shape, range from 0.054
to 1.22 ha, and represent a variety of suburban habitat types such as
alleyways, school yards, vacant lots, parks, and residential areas.
Vegetation at all sites consisted of native herbs (especially
lamb’s-quarters, Chenopodium album ; straggler daisy,Calyptocarpus vialis ; three-lobed false mallow, Malvastrum
coromandelianum ; and tropical amaranth, Amaranthus polygonoides )
and grasses (tumble windmill grass, Chloris verticillata ; plains
bristle grass Setaria vulpiseta ) and the non-native Bermuda grass
(Cynodon dactylon ). Honey mesquite (Prosopis glandulosa ),
anacua (Ehretia anacua ), and sugar hackberry (Celtis
laevigata ) are the most common trees on the study plots (Wall 2014).
Each site is surveyed 8 - 10 times between the end of May and
mid-August. During each survey, we walk linear transects with 2-5
people, spaced 2 meters apart, until we search the entire area of the
site. Surveys typically last 20 minutes to 2.5 hours, and are conducted
between 0800-1200 and 1600-2000, during active periods for Texas horned
lizards (Moeller et al. 2005).
Over the course of six field seasons (2013-2018), predator observations
in and adjacent to our study plots, include frequent (daily or weekly)
sightings of cats (Felis catus ), dogs (Canis lupus
familiaris ), and northern raccoons (Procyon lotor ). We have
found very few snakes, including Texas rat snakes (Elaphe obsoleta
lindheimeri ) (n = 4 sightings), coachwhips (Masticophis
flagellum ) (n = 1 sighting), bull snakes (Pituophis catenifer
sayi ) (n = 1 sighting). Predatory birds are also rarely seen,
red-tailed hawks (Buteo jamaicensis ) (n = 3 sightings), greater
roadrunners (Geococcyx californianus ) (n = 2 sightings).
The Dimmit County ranch located within the South Texas Plains ecoregion
is approximately 32 km North of the Chapparal WMA (wildlife management
area). The habitat is dominated by honey mesquite (Prosopis
glandulosa ) and Acacia thornscrub communities typical of south
Texas shrubland. This relatively wild habitat maintains natural
communities of both predators and prey for Texas horned lizards making
it an ideal site for monitoring natural predation on these lizards. Our
ad hoc observations of predators on the ranch during the summer of 2018,
included a number of potential predators of Texas horned lizards
including: Harris hawk (Parabuteo unicinctus ), red-tailed
hawk, Swainson’s hawk (Buteo swainsoni ), American kestrel
(Falco sparverius ), greater roadrunners, and loggerhead shrikes
(Lanius ludovicianus ), western diamondback rattlesnake
(Crotalus atrox ), bull snake, Texas indigo snake
(Drymarchon melanurus erebennus ), bobcat (Lynx rufus ),
coyote (Canis latrans ), and northern grasshopper mice
(Onychomys leucogaster ).