Foraging movements by the ambush-foraging striped plateau lizard (Sceloporus virgatus) vary between sexes and with air temperature, but not with distance to an immobile observer or time of day

Abstract

AbstractLizard foraging activity is assessed quantitatively by measuring various aspects of activity including number of movements per minute (MPM), proportion of time spent moving (PTM), average speed over an observation period (AS), and speed while moving (MS). With some exceptions, single estimates are given without considering possible effects of environmental variables such as air temperature and time of day. Effects of distance between lizard and observer during observation, the standing distance, have not been studied previously. I measured foraging movements in a phrynosomatid ambush forager, Sceloporus virgatus, early in the breeding season to examine possible effects of sex, air temperature, time of day, and standing distance. Males had higher values of all four foraging movement variables than females. The major cause of this difference is presumably greater socially motivated movement by males, which have much larger home ranges than females. Decreased female foraging probably contributed to the difference because gravid and possibly late vitellogenic females reduce feeding and might become less mobile to reduce the likelihood of being detected by predators when a heavy clutch reduces running speed. Time of day and standing distance did not affect foraging movements. MPM, PTM, and AS decreased as temperature increased, but these effects were small. All pairs of MPM, PTM, and AS were positively correlated, but MS was correlated only with AS, and weakly. I discuss reasons for intraspecific and interspecific correlations among movement variables.