Survival, movement, and fine-scale habitat selection of reintroduced Texas Horned Lizards (Phrynosoma cornutum).
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The historical range of the Texas Horned Lizard (Phrynosoma cornutum) spans most of Texas, and some surrounding states. However, the species has experienced range contraction and population declines throughout much of the range. There is no substantial evidence to specify a single cause, so it is likely the decline has been triggered by multiple factors. Possible threats include Red Imported Fire Ants (Solenopsis invicta), herbicides and pesticides, habitat destruction and disturbance, and collection for the pet trade. Greater conservation effort is needed for Texas Horned Lizards, requiring more detailed knowledge of their habitat requirements. The habitat description given by many researchers is vague, such as that from Burrow et al. (2001): “a mosaic of bare ground, herbaceous vegetation, and woody vegetation in close proximity.” I used radiotelemetry to examine the survival, movement, and fine-scale habitat selection of 23 individual horned lizards released at a reintroduction site in central Texas. The results of my study indicate an early drop in survival within the first few days post-release, followed by a relatively gradual decline in survival over the next 60 – 90 days. Only one of the 23 lizards successfully entered hibernation in the fall. Of the 23 lizards, nine were predated, especially shortly after release by snakes and raccoons. Eight lizards had an undetermined fate because their radio signals were lost. Daily movements were short (mean = 14.49 m, SD = 21.52 m), and home range sizes decreased when the initial locations post-release were removed, indicating lizards dispersed before settling into a home range. My study revealed that Texas Horned Lizards used habitat in similar proportion to what was available on the landscape, but chose locations based on thermoregulatory needs and distance to harvester ant colonies. Overall, reintroduction efforts for Texas Horned Lizards might prove successful because the lizards tend to stay close to the release site and exhibit relatively normal behavior. However, methods to increase survival, such as predator removal and initial release of more lizards, should be used to ensure greater success.