What is the term for the regular social hierarchy found in animal groups?

The term that describes the regular social hierarchy found in animal groups is "pecking order." This concept refers to the established rank order among individuals in a group, determining access to resources such as food, mates, and territory. In many animal species, especially among birds and some mammals, this hierarchy emerges through social interactions and can vary depending on factors like age, strength, and individual behaviors.

Other terms do not relate to the social dynamics within animal groups. For instance, "arrhythmic" pertains to irregularity in rhythm, typically in a biological context, such as heart rhythms, rather than social structures. "Courtship behavior" refers to the specific actions and displays animals use to attract mates, which, while important, do not define hierarchy. "Hydrotropism" describes a plant's growth response to moisture, which is unrelated to animal social structure. Thus, "pecking order" specifically denotes the ranking system observed in social animal groups.