Behavior, Diet and Reproduction in a Desert Lizard, Sauromalus obesus

Chuckwallas living on Black Mountain in the Mojave Desert experienced poor conditions for growth during 1970. After annual plants died and perennials dehydrated in May, the diet of these strictly herbivorous lizards shifted from primarily annuals to perennials only. Chuckwallas stopped eating in late August or September, and entered winter burrows in October after having lost 35% of their body weight during the year. These lizards did not reproduce in 1970, and male home range sizes and aggressive behavior were considerably reduced. Home ranges overlapped extensively, and did not change in size from spring to summer. Chuckwallas were abroad for about eight hours per day in spring, but in summer activity was restricted to about an hour around sunset. Chuckwallas apparently abandon costly social behavior and reproduction in years when succulent food resources are scarce. This may enhance survival of the population during relatively dry years.