Have you noticed how male birds seem to be more brightly colored, with more variation in feathers than female birds?
There are a few reasons this is so, first because male birds must compete with each other for territory, and second so they can attract the attention of a mate.
In competition, males use feather color to warn potential rivals that they occupy a piece of territory. Red-winged black bird males flash hidden red feathers on their upper wings, called epaulets.
Interestingly, scientists have found that when a male's epaulets are dyed black, he is more likely to lose his territory.
When it's time to mate, male birds show off their plumage to attract a mate. In experiments, female birds prefer males with more fanciful feathers, or brighter colors. Scientists think females use male feather color and condition as a way to determine if he is healthy, or will take good care of their nestlings.
For example, the male Pied Flycatcher's color can range from brown to black. Scientists have found that the more food a nestling receives, the bigger and healthier it is, and the blacker its color.