Defensive, climbing, aggressive, and feeding behavior of two sympatric geckos, Coleonyx brevis and Coleonyx reticulatus, were examined. Prey items of both species were identified and the diet of C. brevis was analyzed. In the presence of a predator C. brevis exhibits a defensive behavior involving tail display and body positioning, and during attack tail autotomy occurs. These behaviors plus high frequency of regenerated tails (dd = 68%, 99 = 80%) suggest that this species uses tail display and autotomy to distract predators and escape predation. The absence of defensive tail display, fewer regenerated tails (dd = 25%, 99 = 55%), the presence of a prehensile tail, aggressiveness, and large body size in C. reticulatus suggest alternative predator deterrants and a different tail function. Neither interspecific aggression nor intraspecific aggression in C. brevis was observed. However, intraspecific aggression (tail display, arched back, gular expansion) in C. reticulatus did occur. Both species demonstrate similar foraging behavior (elevated stance, tongue flicking) and utilize visual and chemical cues during foraging and feeing. In C. brevis visual cues are frequently reinforced by chemical cues before attack occurs, however both cues can elicit attack. This strategy may prevent geckos from attacking harmful organisms and may aid them in finding a sufficient amount of prey in a relatively short foraging time. Predominate prey of C. brevis in order of abundance were termites, cicadelids, spiders, solpugids, crickets, and moths. The variety of prey suggest that these geckos forage in several microhabitats and dig or turn items to find prey. Prey items of C. reticulatus were tenebrionid beetles, a grasshopper, and a spider.