Shearwaters and pomarine jaegers are among birds of this type, all of which can be recognized individually by their distinct colors and patterns. The causes for these color variants can be due to mutation, unbalanced diets or disease. Albinism and melanism can often appear on just a part of a bird's body, making it difficult to identify them. As mentioned above, the color of a bird's feathers changes with maturity. Another factor is seasonal changes due to molting.
Most birds molt completely at least once a year.
But large birds such as eagles or cranes may take some years to molt entirely. They molt completely only once a year, and aside from the natural effects of wear and tear, there is no distinction between summer and winter plumage. In another example, mature white wagtails molt entirely after breeding, which gives them winter plumage. Then again in the spring, molting occurs in specific areas, such as the breast and head, to prepare the bird for the onset of summer plumage. Male ducks molt entirely after the breeding season when their plumage becomes more subdued like female ducks.