Male mating strategies and the mating system of great-tailed grackles

Great-tailed grackles (Quiscalus mexicanus) are sexually dimorphic, dichromatic, colonially nesting blackbirds. In this study, males pursued three basic types of conditional mating strategies, each of which employed a different set of mating tactics. Territorial males defended one or more trees in which several females nested. They achieved reproductive success by siring the offspring of their social mates and through extrapair fertilization. Resident males lived in the colony but did not defend territories or have social mates. Transient males passed through the colony, staying no more than a few days, and probably visited more than one colony. Residents appeared to queue for access to territories, but transients did not. Residents and transients gained all paternity through extrapair fertilizations and provided no parental care. Territorial males sired the majority of offspring, but residents and transients also sired small numbers of nestlings. Territorial males were larger and had longer tails than nonterritorial males. The number of social mates was related to body size, and males that sired nestlings were heavier and had longer tails than males with no genetic reproductive success. Males that gained paternity through extrapair fertilization were heavier and had longer tails than males that did not. The mating system of great-tailed grackles can best be categorized as non-faithful-female frank polygyny.