ECOLOGY OF THE BEADED LIZARD, HELODERMA-HORRIDUM, IN A TROPICAL DRY FOREST IN JALISCO, MEXICO

Activity patterns, diet, resource use, and thermal biology were investigated with the use of radiotelemetry in a population of Mexican beaded lizards in a tropical dry forest in coastal Jalisco, Mexico. Fifteen H. horridum ranging in mass from 36 to 1600 g were captured and marked within a 36 ha area. Growth rates of up to 15.5 mm/yr were observed. Diet consisted of eggs of spiny-tailed iguanas and other reptiles, and bird eggs and nestlings. Shelters were used in arroyos, on hillsides, and the forest floor. Trees were often used as shelters during the wet season. Mean home range size was 21.6 ha. Beaded lizards had a primary peak of surface activity at 1800 h, and a smaller peak at 0900 h. Seasonal differences in daily activity times were noted. Peak seasonal activity (17 d/mo) occurred in May and gradually decreased through the summer to a low of 1 d/mo in January. Beaded lizards, on average, spent 67 min above ground and traveled 236 m per activity bout, resulting in approximately 120 h/yr invested in surface activity. Minimum and maximum body temperatures recorded for resting H. horridum were 17.7 C (January) and 37.2 C (June). Mean monthly body temperatures ranged from 19.9 C in December to 28.5 C in July. Activity temperature range was 22.5-36.0 (xBAR = 29.5 C). Activity temperatures were lower during the wet (xBAR = 27.0) than during the dry (xBAR = 30.2) season. Heloderma horridum is a more active, semiarboreal lizard than is H. suspectum, the only other living helodermatid.