Sexual selection, plumage ornamentation and behavior of Gambel's and Scaled quail

I examined female mate choice and male-male competition in two congeneric species of New World Quail: Gambel's Quail (Callipepla gambelii), a sexually dichromatic species in which males exhibit multiple plumage ornaments, and Scaled Quail (C. squamata), a monochromatic, unornamented species. Mating decisions of female quail were unrelated to male plumage. Likewise, most plumage ornaments did not correspond to winners of male-male competition. In a free-ranging population of Gambel's Quail, male plumage also did not correlate with pairing date or male dominance. Thus, the relative strength of sexual selection in these two species does not adequately explain striking differences in plumage dichromatism. If plumage ornaments do not signal male condition, they may not function in sexual selection. Alternative hypotheses may be required to account for multiple ornate traits in males. Unlike most ornaments, head plume manipulations in Gambel's Quail influenced the outcome of male-male competition. Plume position (up vs. down) also correlated with dominance. Head plumes may signal a male's aggressive intent.;Winners of female choice and male-male competition displayed at high rates. Manipulating the display rates of males altered female mating decisions. Such behavior appears to be mediated by testosterone and may reflect male quality. Castration eliminated or decreased display rate.;Body-size also influenced male contests; larger males of both species dominated smaller individuals. Like display rate, body-size may indicate male quality. In a free-ranging population of Gambel's Quail, male mass was the only trait that correlated with male dominance, early pairing and successful breeding.;Although sexual selection in both quail species favored high display rates and male body size, some interspecific differences were observed. Female Scaled Quail typically chose dominant males, whereas female Gambel's Quail did not. During male-male competition, Gambel's Quail exhibited higher levels of aggression than Scaled Quail. Such differences may reflect differing social systems. Scaled Quail appear have high levels of social (and presumably genetic) monogamy, suggesting that pair bonds and dominance status of males may be stable. In contrast, both male and female Gambel's Quail can exhibit sequential associations with multiple mates, indicating that relationships between individuals may be more flexible.