Lizards in the genus Sceloporus have evolved two distinctive types of headbob displays: the well-studied “push-up display”, used mainly as a broadcast along territorial boundaries and also during aggressive encounters, and a “shudder-bob” display, exhibited primarily by males during courtship (Carpenter & Ferguson 1977; Martins 1993). The two displays involve similar motions (raising and lowering of the head and body), but vary in both structure (the timing of the motions that comprise the signal) and the context in which they are used. Furthermore, push-ups and shudder-bobs differ in terms of the interspecific variation in structure they exhibit. Specifically, the push-up display exhibits considerable and consistent variation in the pattern of motion exhibited by species, whereas shudder-bob displays appear to be uniform in structure across species (Carpenter & Ferguson 1977; Ruby 1977).