The kinds of traits involved in male--male competition: a comparison of plumage, behavior, and body size in quail

Abstract

I compared the role of ornate plumage, behavior, and body size during male–male competition in two species of New World quail. Gambel’s quail (Callipepla gambelii) is a highly ornate and dichromatic species, whereas scaled quail (C. squamata )i s unornamented and monochromatic. During paired contests between unfamiliar males, high rates of testosterone-mediated behaviors (tidbitting, calling) and large body size (mass, tarsus, and tail length) corresponded to winners. In the highly ornate Gambel’s quail, male head plumes also influenced the outcome of contests. Plume enhancement made Gambel’s quail more likely to win contests, whereas plume removal made males more likely to lose. Plume position also reflected male status. Winning males erected plumes, whereas losers frequently flattened them. Some plumage ornaments, such as belly patches, did not play a primary role during male contests. Unlike static ornaments, head plumes are highly modifiable and likely signal immediate information regarding a male’s intent, similar to a coverable badge. Combined, intrasexual selection favored dynamic traits (fast display rates, modifiable ornaments) and static traits (body size) as indicators of male condition or motivation. In scaled quail only, male size was favored both by male–male competition and female choice. Accordingly, the degree of size dimorphism (tarsus length) is greater in scaled than in Gambel’s quail. The frequency of overt aggression (chases, pecks, displacement) also differed between species. Gambel’s quail were very aggressive, and subordinates often challenged their opponents. In contrast, scaled quail were less aggressive, and subordinates rarely disputed rank. Interspecific comparison indicated differences in the maintenance of male status and possibly in the honesty of signaling. Both appear to be related to differences in social system.