Natural History Notes on Crotaphytus wislizeni (Reptilia: Iguanidae) in Colorado

The leopard lizard, Crotaphytus wislizeni, was studied in Mesa Co., Colorado, during the summers of 1961 to 1963. Scattered populations, restricted to the valley of the Colorado River below 5,000' elevation, date from post-pluvial (± 11,000 years) eastward dispersal. The populations occur in greasewood-grass, big sage-grass, and saltbush associations, on sand and clay soils. Mammal burrows are used for thermal escape and as overnight retreats. Adults emerge from hibernation in May and are active for approximately three months. Diel activity starts as early as 7:30 AM, is interrupted by excessive temperatures around 12:30 or 1:00 PM, resumes about 4:30 PM, and lasts until dusk. Individuals habitually use certain burrows and basking stations, but there is no apparent territoriality. Mating was observed on 20 May and 2 June, and eggs are laid by the end of the first week of July. The single clutch averages 7.3 eggs (N=10). Incubation takes five to seven weeks and hatchlings appear in early August. Hatchlings average 44.6 mm SVL at emergence, and grow to 55 mm SVL before hibernation (one month). Both males and females are mature at the start of their third season, when 22 months old and 80 to 90 mm SVL. Females are larger than males at all ages over nine months. Leopard lizards eat large and active arthropods and several species of lizards.