Why do some birds have breeding plumage even in non breeding season while some birds don't?

In case of birds, some birds develop their “breeding plumage” morph in their respective breeding season. But why do some birds like Indian paradise flycatcher male possess such breeding plumage morph throughout the year/life? Won’t this make the bird more exposed to their respective predators. Why do they carry breeding plumage morph even in non breeding season? Why did evolution favoured such phenotype?

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The traditional argument is that the ancestral state is to only molt once per year, with an additional molt (or two) as a derived state. So it’s possible that some groups simply didn’t develop a non-breeding plumage. A few other considerations – if the breeding season doesn’t match the molt timing, then it’s hard to have separate breeding and non-breeding plumage. Also, many birds maintain territories in the winter. If the plumage functions in territorial behavior as well as mate selection, then it would make sense not to lose that plumage.

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So if we consider that a bird maintains a specific plumage even outside of its breeding time. So then it might serve several functions other than functions related to breeding

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Fascinating topic! In consideration of those birds that overwinter in my area, with the exception of the fall brood juveniles and gold finch males, the others that do not migrate who are visually distinct in plumage male to female seem to maintain “breeding” distinctions, though somewhat muted. A study queried by New Scientist suggests a relationship between pale feathers in migration and the distance the birds travel attributing the light feathers to temperature control. We see in blue birds that migrate over short distances that the males maintain their bright blue plumage in migration having changed their feathers in the fall; however, the male ruby throated hummingbird that migrates all the way to Mexico also molts after breeding and maintains the adult coloration. If you are interested in the article here is the url: Birds feathers: Migratory species may have paler plumage to help them keep cool | New Scientist

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Are these the same birds that stay in mated pairs in the winter.

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I won’t make an interesting argument about this, but here in Mexico i’ve only seen migratory birds molting their breeding plumage. Resident species stay with the same plumage year-long. Don’t know why, I’m basing this only on experience.

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In my view of evolution, a phenotype may not confer an advantage, but if it does not present a disadvantage it persists. Many birds do not have breeding plumage, many do. I don’t know why this happens, but both seem ‘successful’ in terms of evolution. As far as we know!
Others may not share this view.

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But how do we can say that if a particular phenotype doesn’t serve any disadvantage then by part it’s an advantage for them. But won’t that phenotype expression accumulate unnecessary part of genome?

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We don’t know. But the fact that traits persist suggests that they are not specifically disadvantageous. Whales retain the basic mammalian design, even to a vestigial pelvis, in spite of resembling fish. It’s as though types of life need to work within a set of constraints. There is no advantage to doing this, but as long as it does not represent a major disadvantage, the form will persist. I have no idea why some birds have breeding plumage and some do not. It’s just how they work, either way seems to be successful, so it may or may not change.

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