Breeding plumages

Through out the year birds change their plumage from their mating plumage to their regular plumage which is usually a duller version that allows for better camouflage with their landscape. The breeding plumages of birds vary immesnly and usually are incredibly exuberant and flashy. Females don't usually have any breeding plumages and are dull compared to the males, the reason for this is because since they are on a nest they have to blend in much more than that of a male so if they were brightly colored they would have a disadvantage of having to stay in one spot for such a long time.

Male wood duck

As you can see this plumage is a lot more flashy than that of the female, this as explained above is because the female has to sit on a nest during incubation.  

Female Wood Duck

Female Wood Duck, as you can see is not very flashy and can blend in pretty well in the landscape.

Male Tree Swallow

The Male tree Swallow has a much bluer back than that of the female it is also glossy. Unlike the wood duck above the male Tree Swallow will keep this plumage throughout the year while the male Wood Duck will Molt.

Female Tree Swallow

The female here is brownish and darker and less glossy than that of the male this is for the same reason as the female wood duck and it is an evolutionary advantage to be a duller color.