Factors Affecting Activity in Sceloporus Virgatus

Abstract

A population of Sceloporus virgatus, an iguanid lizard, was studied to determine the adult patterns of activity and inactivity. Activity was primarily a function of the sex and age of the individual, as well as reproductive condition. Activity was highest during the breeding season when males were active daily (97% of the days) and females were active 76% of the days. Males were also active longer and moved greater distances than females. Males lost mass during this high activity period. During the nonbreeding season, females were active more days than males. Activity levels were not substantially different for females during the breeding and nonbreeding season. Male activity decreased dramatically during the nonbreeding season and activity differed depending on the age of the lizard. Year—old males were nearly twice as active as older males (57% compared to 29% of the days). Activity was so low in these large, older males that territory maintenance was probably no longer functional. This low activity suggests that male territories are primarily for breeding purposes rather than for feeding in this species. These data indicate that inactivity is part of a lizard's adaptive strategy and not merely a response to inclement weather. Inactivity decreases an individual's risk of predation and conserves energy, thereby increasing an individual's chance of survival and future reproduction. Lizards were presumably active when the benefits of activity exceeded its costs and risks.