Final answer:
Red plumage in cardinal males is common because it is attractive to females and is an honest signal of the male's quality, aiding in reproductive success despite potential survival costs.
Step-by-step explanation:
The alleles conferring red plumage to cardinal males are common because red plumage is preferred by female cardinals in choosing a mate. This preference is known as sexual selection, a form of natural selection where certain traits become more pronounced because they aid in attracting a mate for reproduction. In this case, the colorful plumage is an honest signal of a male's quality, and the brighter the plumage, the more attractive the male is to potential mates.
Moreover, while there are species where colorful plumage might hinder survival by making males more visible to predators, the advantages in reproductive success generally outweigh these potential costs. In the case of species like the cardinal or the peacock, the distinctively colorful feathers help males in attracting females and may also help in other functions such as defending territory, as seen in robin species.