Studies on the natural history and ecology of sympatric whiptail lizards (Cnemidophorus marmoratus and C. tesselatus) from Madera Canyon (Brewster County, Texas)

This study addresses various aspects of the natural history and ecology of Cnemidophorus marmoratus and C. tesselatus (Squamata: Teiidae) from Madera Canyon, Texas (Brewster County), located on Big Bend Ranch State Park (Chih uahuan Desert). The mean snout/vent length (SVL) was 83.1 mm for C. marmora tus, and 85.1 mm for C. tesselatus. Actively foraging lizards of both speci es hall similar cloacal temperatures They are generalist predators that fee d on a variety of arthropods, and there was a high degree of dietary overla p between the two species (D = 0.78). Major prey species included beetles ( 26 - 38%), orthopterans (24 - 25%), termites (9 - 12%), lepidopteran larvae (9 - 11%)and spiders (8 - 11%). There was a high degree of overlap in temp oral periods of activity between these two whiptails (D = 0.71, spring; 0.7 8, summer). Most lizards were observed basking between 0700 - 0830 hr CST, with peak activity to 1059 hr. Activity decreased markedly after 1300 hr. W ith respect to microhabitat preferences, C. marmoratus was most frequently associated with open sandy areas, whereas C. tesselatus preferred foraging near rocks exposed to the sun or within shaded areas of rock cover. Tongue- flicking rates when foraging and when in close proximity to conspecifics we re significantly higher in C. marmoratus. The potential for interspecific c ompetition between these two lizards in Madera Canyon is high.