Contextual use of the push-up display by the sagebrush lizard, Sceloporus graciosus

The push-up display has been categorized into 'Assertion' and 'Challenge' displays on the basis of hypothesized function. Assertion displays are spontaneous displays given in the absence of a direct audience, and may be used to broadcast information about the identity of the displaying animal. Challenge displays are of greater intensity and are produced in the presence of territorial intruders. These differences have not been described or quantified explicitly, and the specific meaning or information content of these displays has not been examined in any detail. In this study, I examine the social and behavioural contexts in which the push-up display of Sceloporus graciosus is produced. Focal-animal observations of both male and female lizards in the field show that lizards of both sexes produce structurally different types of push-up displays in different contexts. Certain body postures that expose the blue belly and gular patches are used only in push-up displays produced during agonistic, territorial interactions. Displays used during courtship do not include the use of these body postures, and include slightly fewer head-bobs and fewer legs being extended. Displays produced in the absence of a direct audience are more variable but tend to include even fewer head-bobs, fewer legs extended, and less frequent use of specific body postures. Also, lizards tend to produce push-up displays following bouts of locomotion, and the fine structure of the display is related to the distance traversed immediately before the display is produced.