An Ecological Study of the Chuckwalla, Sauromalus obesus Baird, in the Western Mojave Desert

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Abstract
A marked population of chuckwallas, Sauromalus obesus, was the object of an ecological study in the western Mojave Desert during three activity seasons. The results include data on diel and seasonal activity, reproduction, size, growth, age, sexual dimorphism, molting, population dynamics, and feeding. Members of a second population located during the last year of study were collected to supplement the data on reproduction and to provide specimens for a color and pattern analysis. This herbivorous lizard inhabits rocky areas and exhibits daily activity typical for heliothermic reptiles. Chuckwallas are active only from mid-March to mid-Aug. and presumably estivate and hibernate during the inactive period. Both sexes live within home ranges, but the consistent occupancy of a home was not observed. All mature males are re-productively active during the spring. Data suggest that mature females do not produce a clutch of eggs each year, but rather every two years or more during the middle of June. The chuckwalla population exhibits an even sex ratio, low density, low reproductive potential, a high survival rate, and great longevity. Most growth occurs during the spring, the time of maximum vegetational development. Although chuckwallas probably grow throughout their life, the high-growth rate occurs among juveniles. Sauromalus obesus was compared with Dipsosaurus in order to ascertain features of special adaptive significance.

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