FACTORS INFLUENCING THE SELECTION OF BASKING PERCHES ON CARDON CACTI BY SPINY-TAILED IGUANAS (CTENOSAURA-HEMILOPHA)

The selection of optimal basking perches to achieve preferred body tem peratures and avoid predation risks is one of the most important behav ioral decisions that a lizard makes. We studied perch selection by the spiny-tailed Iguana (Ctenosaura hemilopha) in Baja California Sur whe re they bask on elevated cacti. The more important factor determining cardon selection by iguanas was the presence of old woodpecker holes w hich could be used as refuges within the top 50 cm of a branch. Other factors are the height of the cardon, the presence of some other holes and the number of branches of the plant. These data suggest that pred ation risk is the strongest factor affecting the selection of certain cardons as basking structures by spiny-railed iguanas. Because the hol es are mainly old woodpecker nests, the choice of a cardon as a refuge -perching sire has to be related to a prior selection by woodpeckers.