Aggressive behavior is observed through, approaches, lunges, pursuit of enemies, back arching, fighting, and biting. If mate guarding fails, the male companion is not displaced, but will face sperm competition. They eat fewer prey in order to accomplish this task, not because food is shared with females, but likely in order to stay close to the female, or to signal genetic fitness. This male declined ingestion rate was found not to be further affected by larger body weight, following a larger female, or fending off more aggressions. Following a larger female however resulted in increased aggression, attributed to the female's fecund. Oviposition Western Mexico whiptail lizard are oviparous (producing eggs that develop and hatch outside the maternal body). Females reproductive event varies, from a single clutch up to three clutches annually, with range of clutch size of 1~5 eggs. Clutch size and size of female are positively correlated. And males tend to compete more intensely for larger, more fecund females. But in general, Aspidoscelis lizards, especially striped species such as costatus, tend to be active foragers, always in search of their prey. Due to their active foraging strategy, body shape, and escape strategies, species in the genus Aspidoscelis tend to show a relatively small clutch size, proportional to their body mass. Site Selection Expecting females dig holes (referred to as nest) in the soil, often under rocks, about 32 cm long and 14 cm wide, in which the oviposition takes place. After clutch of eggs are laid, the female whiptail would not cover the clutch with soil, which likely enable the hatchlings more freedom to leave the cavity. [23] The female lizard would then leave without incubation or guarding the nests. No further parental care is provided. The clutch is left to incubate under a most favorable environment, a moist and warm nest, with minimal temperature fluctuations under rocks, selected by the female lizard.[23] Eggs typically take 60 to 75 days of incubation to hatch. Juveniles usually hatch during July or August. Relationship with Humans When human visitors approach and they feel threatened, the lizards would burst into motion, run across the arid land and disappear behind the closest low scrubs or rock. They are fast runners and hard to catch. If human hold them in their hands, the whiptail may attempt a harmless bite. Conservation Status In 2007, Aspidoscelis costatus are listed as “Least Concern”, following IUCN criteria. According