Castration in Gambel's and Scaled Quail: Ornate plumage and dominance persist, but courtship and threat behaviors do not

During the breeding season, testosterone in male birds is often linked to s ome secondary sexual ornaments, courtship behaviors, and intrasexual aggres sion. I examined the effect of castration on plumage expression in Gambel's Quail (Callipepla gambelii), a species in which males are highly ornate, a nd in Scaled Quail (C. squamata), an unornamented species. Using male pairs , each consisting of a castrate and a control, I also assessed whether cast ration affected (1) the behavior of males, (2) the mating decisions of fema les, or (3) the outcome of male-male competition. Castration did not alter the plumage of male Gambel's or Scaled Quail. in these species, and some ot her members of the avian order Galliformes, production of ornate plumage ap pears to be independent of testosterone. In contrast, castration reduced or eliminated courtship behaviors. Females almost never preferred castrated i ndividuals. During male-male competition, castrates also exhibited lower ra tes of threat behaviors, which appear to be identical to those used during courtship. Castration did not, however, influence the outcome of male-male competition. Castrates of both species exhibited overt aggression (pecks, c hases, displacement) and frequently won male contests. Such results suggest that certain types of aggressive behavior may be testosterone-independent. In both Gambel's and Scaled Quail, male body size correlated positively wi th dominant individuals. (C) 2001 Academic Press.