Great Basin Naturalist


A mark-recapture study of the short-horned lizard (Phrynosoma douglassi) and the sagebrush lizard (Sceloporus graciosus) was performed from 1976 to 1977 in southeastern Idaho. Both species had mean cloacal temperatures of approximately 33 C. However, P. douglassi had more variable cloacal temperatures, particularly during morning and evening periods. This was caused by differences in sleeping sites chosen by the two species. Adults of both species were active from mid-April through late August, with peak activity in June. Juvenile P. douglassi displayed a seasonal activity pattern similar to that of adults. Juvenile S. graciosus were most active later in the year (August), when adults were disappearing. In both species, young-of-the-year appeared in early to mid-August. Adult and juvenile P. douglassi were active during all daylight hours and displayed no activity peaks, whereas young-of-the-year displayed a bimodal activity pattern. Adult and juvenile S. graciosus were active over all daylight hours but had peak activity between 1200 and 1500 h. Ants (Pogonomyrmex) were the lizard's principle prey. However, only young-of-the-year P. douglassi had activity patterns that paralleled that of ants on their mounds.