"Pecking order" is the colloquial term for a hierarchical system of social organization. (...) The original use of pecking order referred to the expression of dominance in chickens. Dominance in chickens is asserted by various behaviours, including pecking, which was used by Schjelderup-Ebbe as a measure of dominance and leadership order. In his 1924 German-language article, he noted that 'defense and aggression in the hen is accomplished with the beak'"