About Ctenosaura hemilopha (Cope, 1863)
The cape spinytail iguana, Ctenosaura hemilopha, is green or yellow when young, and becomes whitish gray as it ages. Mature individuals may be white or light gray with black chevron markings, and their color can change based on heat conditions or the individual's temper. Males reach a maximum total length of 100 centimeters (39 inches), while females are typically 30% smaller, reaching 70 centimeters (28 inches). Males grow large jowls and a dorsal crest composed of larger dorsal spines, making this species sexually dimorphic. One theory holds that cape spinytail iguanas were brought to the Baja peninsula and its nearby islands by early Seri Indian inhabitants thousands of years ago, who transported them from the mainland as a food source. This theory is supported by the observation that the species' mainland coastal distribution ends 115 kilometers south of Isla San Esteban. Contrary to predictions from ecological niche theory, this species coexists with the giant San Esteban chuckwalla on San Esteban Island. The two species forage for the same plants in the same habitat, at the same time of day, and during the same season, with neither species displacing the other. Cape spinytail iguanas make their dens in old woodpecker nests inside giant columnar cacti, as well as in other tree cavities. The most important factors for a lizard choosing a cactus as a den site are the presence of other existing holes and the height of the cactus, as these refuges let lizards feed and bask on the cactus while minimizing predation risk. The existence of both mainland and island populations of this species has been valuable for biologists, who use these groups as study and control groups to compare the evolution of island populations.
