Factors Influencing the Selection of Basking Perches on Cardon Cacti by Spiny-Tailed Iguanas (Ctenosaura hemilopha)1

The selection of optimal basking perches to achieve preferred body temperatures and avoid predation risks is one of the most important behavioral decisions that a lizard makes. We studied perch selection by the spiny-tailed Iguana (Ctenosaura hemilopha) in Baja California Sur where they bask on elevated cacti. The more important factor determining cardon selection by iguanas was the presence of old woodpecker holes which 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 predation risk is the strongest factor affecting the selection of certain cardons as basking structures by spiny-tailed iguanas. Because the holes are mainly old woodpecker nests, the choice of a cardon as a refuge-perching site has to be related to a prior selection by woodpeckers.