 In at least one hummingbird species – the green-backed firecrown ("Sephanoides sephaniodes") – flower colors preferred are in the red-green wavelength for the bird's visual system, providing a higher contrast than for other flower colors.Further, the crown plumage of firecrown males is highly iridescent in the red wavelength range (peak at 650 nanometers), possibly providing a competitive advantage of dominance when foraging among other hummingbird species with less colorful plumage.The ability to discriminate colors of flowers and plumage is enabled by a visual system having four single cone cells and a double cone screened by photoreceptor oil droplets which enhance color discrimination.