Female frogs are larger than males in about 90 percent of species. Larger females have a reproductive advantage because they can store more energy and produce larger clutches. In species in which males are larger, males compete physically for calling sites and mates, giving larger males an advantage.
Males of most frog species have vocal sacs and use calls to attract and court females and to intimidate other males. The initial attraction calls give information about the species, size and sexual readiness of the calling male. Females are also attracted to males based on the coloring of the vocal sac and the size of the forelimbs and thumb pads, which are important to successful mating. Females of brightly colored species prefer the brightest colored males.