The Texas Horned Lizard (Phrynosoma cornutum) is a species of special conservation concern in Texas and the southwestern United States.This study was designed to compare capture rates of adult female and male Texas Horned Lizards by time and month. Horned lizards were captured by road cruising at Chaparral Wildlife Management Area in southern Texas. We found a female bias in morning capture rates compared with evening capture rates. These sex-specific differences in timing of activity may indicate an important difference in physiological constraints on the sexes. Sex-biased movement patterns must be accounted for in population sampling and plans to conserve this imperiled species.