Final answer:
In a species of bird where males have brightly colored feathers and engage in polypous mating, the most likely form of sexual selection is intersexual selection, where female birds select their mates based on traits like plumage coloration.
Step-by-step explanation:
In a species of bird with a strongly polypous mating system and males with very brightly colored feathers, the most likely form of sexual selection would be intersexual selection. Intersexual selection occurs when females choose their mates based on certain traits, such as brightly colored plumage, which are indicative of the male's fitness and genetic quality. This form of sexual selection is observed in many bird species where the male displays his colorful feathers to attract a mate. The bright colors suggest that the male is healthy and capable of producing healthy offspring. In contrast, intrasexual selection, which involves male-to-male competition, is less likely to be the predominant form of sexual selection in this scenario since brightly colored feathers are typically used to attract females rather than deter competing males.