International Journal of Comparative Psychology

While the behavior of many animals can be identified as involving discrete and stereotyped actions, there is a persistent tension between emphasizing the fixedness of the actions (“Fixed Action Patterns”) and emphasizing the variation in the components comprising those actions (“Modal ActionPatterns”). One such action, the back and forward judder of crickets often exhibited in agonistic interactions, was analyzed. Judders occurring on a horizontal surface by Gryllus bimaculatus were compared to those occurring on an inclined platform. Although the body movements involved were variable, that variability occurred in the context of maintaining some features of judder invariant. For example, the crickets maintained their bodies so that they were horizontal relative to the substrate, not to gravity, and most features of the back and forward movement (e.g., distance moved, velocity) were maintained as fixed despite differences in posture and movement. At a theoretical level, what these findings suggest is that behavior patterns involve a combination of fixedness and variation in the service of that fixedness. It becomes an empirical issue to discern these complementary components.