Chromatic and achromatic differences of melanin- and carotenoid-based plumage coloration in five minivet species (Pericrocotus spp.) under conspecific and predator visual systems

Adaptive mate choice has been accepted as the leading theory to explain the colorful plumage of birds. This theory hypothesizes that conspicuous colors act as signals to advertise the qualities of the owners. However, a dilemma arises in that conspicuous colors may not only attract mates, but also alert predators. The "private channels of communication" hypothesis proposes that some intraspecific signals may not be visible to heterospecific animals because of different visual systems. To better understand the evolution of plumage colors and sexual selection in birds, here we studied the chromatic difference and achromatic differences of melanin- and carotenoid-based plumage coloration in five minivet species (Pericrocotus spp.) under conspecific and predator visual systems. We found that either the chromatic or achromatic difference among male or female minivets' plumage was consistently higher under conspecific vision than under predator vision for all five studied species of minivets. This result indicated that individual differences in plumage colors of minivets were visible to the conspecific receivers and hidden from potential predators as a result of evolution under predation risk and conspecific communication. However, males were under a higher risk of predation because they were more conspicuous than females to the vision of a nocturnal predator.