Final answer:
Brightly colored plumage in male birds can increase their fitness by attracting females and signaling genetic fitness. This increases the chances of successful reproduction and access to resources.
Step-by-step explanation:
Males of some bird species use bright and colorful plumage to increase their fitness. This is because colorful feathers attract females and signal to them that the male is healthy and genetically fit. Females are more likely to choose males with bright feathers as mates, which increases the chances of successful reproduction. Additionally, bright plumage can help males establish dominance and defend territories, giving them better access to resources and increasing their overall fitness.