Variations in plumage can be based on the sex of the bird, its age, or seasonal changes caused by molting. Molting patterns are complex and even the experts do not have all
the answers about how this process is controlled. This basic introduction to molting will provide you with a
glimpse into the challenge and fun of studying molting patterns and the
range of molting behaviors.
Several plumage patterns can be observed in birds. The molting process can be either very obvious or difficult to detect, depending on the species and its plumage pattern.
Young birds pass through one or more subadult plumages before reaching full adult plumage, referred to as the bird's definitive plumage.
The number of years required for a species to reach its definitive plumage varies widely. Many songbirds reach adult plumage after one year. Some gulls take as long as four years to reach adult plumage, and some eagles can take as long as five years to reach full adult plumage.
Adult birds--single plumage pattern:
In the simplest case, both male and female birds look alike and retain their definitive plumage throughout the year. Both the Blue Jay and Cedar Waxwing fall into this category. Birds with this plumage pattern do molt, but the new feathers have the same coloration and pattern as the previous plumage.
Adult birds--seasonal variation:
Some adult birds (typically the males) sport a bright, colorful plumage in the spring, which is replaced by more subdued colors during the post-nesting molt. The widespread American Goldfinch provides a good example of this plumage pattern. In its basic plumage the male goldfinch is similar in appearance to the female.
Try your hand at identifying these ten species in their nonbreeding plumage.
Adult birds--sexual dimorphism:
Males and females of some species have such different plumages that it would be easy to think they were two different species. The Painted Bunting, shown below, is a case in point. In many species exhibiting strong sexual dimorphism, young males resemble the females until they are one or two years old.