“Plumage” comes from the Old French meaning feathers or appearance. Today the word is almost exclusively used for a bird’s set of feathers. Depending on the species, birds have various plumages throughout the year. Feathers wear out, are broken, or lost and they need to be replaced on a regular basis, and in the process there might be two or more plumages over a year or even several plumages over several years. This makes things a bit more challenging for birdwatchers as dull winter plumage warblers are much more difficult than those in colorful breeding plumage.
There are several types of plumages in a bird’s life cycle. They are born nearly naked as are songbirds or with “natal down” or natal plumage like that of ducklings or chicks. The purpose of these feathers is mainly insulation. After a few days or weeks or months depending on the species, the young birds develop what is called juvenile, sometimes “juvenal”, plumage, and keep it until fall. Often the young resemble the winter or female plumage of the species.
In the case of songbirds, the young keep their juvenal plumage until the spring or may molt into a sub-basic plumage that shows some of the breeding coloration. Then, early in the spring they molt into their most colorful breeding or courtship plumage. When the sexes are dimorphic (have different plumages), the male is typically the most colorful. In the case of gulls, hawks, eagles, and other species, the birds make take several years to develop their breeding plumage. The Red-tailed Hawk, for example, takes about three years to develop its red (actually rufous) tail.
According to the Southwestern Bald Eagle Management Committee “During its first four weeks of life, an eaglet’s fluffy white down changes to a gray wooly down. At about five weeks, brown and black feathers begin to grow. It becomes fully feathered at 10 weeks of age. In its first year, the mostly dark-colored juvenile can often be mistaken as a golden eagle. However, the bald eagle progressively changes until it reaches adult plumage at five years. Its dark eye lightens throughout its first four years of life until it becomes yellow and its beak changes form gray-black to a vibrant yellow.” The adult eagle wears a plumage of 5000 to 8000 feathers.
After the mature plumage is reached the bird then moves back and forth between its basic plumage and its breeding plumage. The basic plumage makes the bird less visible to predators during the non-breeding season. Often the males and females look a lot alike at that time.
Feathers obviously have several functions, so molting is required to keep the plumage in good condition. But it costs a lot of energy. One study of the Chaffinch estimated that the birds metabolism has to increase by about 40% to produce new feathers, depending on the temperature. That’s replacing something like 1500 to 3000 feathers, typical of songbirds. That is an enormous burden at an enormous cost, but obviously well worth it.
Then think about the swan that has to replace 25,0000 feathers!
Then think about the person assigned the task of counting all these feathers!