39 



New Mexico-Arizona border along the PortaJ Road, Cochise County, Ari- 

 zona. A pitfall trap grid covering one hectare was established. The 

 site was at an elevation of 1500 m., with sandy soil and a few scatter- 

 ed rocks, dissected by numerous shallow, poorly defined washes. Proso - 

 pis and Ephedra were the dominant plants, with Acacia, Flourensia , Gu - 

 tierrezia and Bouteloua . Plant cover was 15-20%, increasing to 30-35% 

 after summer rains. Heteromyid rodent mounds and burrows were numerous 

 and a major source of shelter. Eight other lizard species were sympa- 

 tric, none of them congeneric. Daily activity was bimodal; 75% of cap- 

 tures occurred between sunrise and 1130 hours with the remainder occur- 

 ring between 1730 and 1930 hours. This pattern broke down on cloudy 

 days. Rainfall depressed activity for as much as 2^^-36 hours after 

 heavy rains (more than 3 cm). Seasonal activity peaked the first year 

 during the second half of June with an average of 17 lizards per day 

 handled, and declined to 3.5 lizards per day handled during the second 

 half of August. Seasonal activity was steady throughout the second 

 year, ranging from an average of 2.5 to k.5 lizards handled per day. 

 Roadrunners, burrowing owls and loggerhead shrikes were observed to 

 prey successfully on _C. uniparens ; remains were found in the stomach 

 of Crotaphytus wislizenii. Potential predators are discussed. Tail- 

 break frequency increases in older age classes; the overall percentage 

 is 15.6, which is low compared to _C. tigris . This is possibly due to a 

 higher success to attack ratio for _C. uniparens predators and differen- 

 ces in life-spans between the two species. Mature females range from 

 58 to 77 mm in snout-vent length (mean SVL is 65.5+3.9 mm). All liz- 

 ards are reproductive by early June; reproduction continues through the 

 first half of July, then rapidly drops off and ceases by early August. 

 Clutch size ranges from i-k with a mean value of 2. 77+. 06. There is a 

 significant positive correlation between clutch size and SVL. Two, 

 possibly three clutches are produced annually; clutch intervals varied 

 from 21 to 28 days. No significant correlation existed between SVL and 

 egg size or egg weight. The total clutch weight/body weight ratio ran- 

 ged between 9.6-20.0 (mean l^.'f+.2^). Forty-seven lizards had home 

 ranges entirely within the study area; home range size wcis not correla- 

 ted with either the number of recaptures or SVL. Mean home range size 

 differed highly significantly between the two years. The mean home 

 range size was 815+88 m^ (range 120-2386) for the first year and ^17+62 

 m^ (range 2^0-7^*6) for the second based on 39 and 8 lizards, respectiv- 

 ely. Normal rainfall preceded the first study season whereas the se- 

 cond was preceded by very heavy precipitation, which greatly increased 

 the production of desert annuals and their invertebrate herbivores. 

 Apparently _C. uniparens responded to increased prey availability by re- 

 ducing the average home range size. No territoriality nor aggressive 

 behavior was observed; lizards forage, seek shelter, and fall into the 

 same pitfall traps without paying the slightest overt attention to each 

 other. Growth rates remained the same over the entire study period; 

 differences in prey availability did not influence the volume of prey 

 consumed. Growth rates were negatively correlated with SVL. A sharp 

 decline in growth rate occurs with the attainment of reproductive ma- 

 turity. Density estimates of adult lizards for the 2 years were 103+6 

 and 78+12 per hectare; the total number of lizards marked was 135 and 

 138 and the number of different individuals recaptured was 98 and 82, 



