Why Do Goldfinches Change Color? Summer vs Winter Plumage

Two molts a year: how the change happens

Birds cannot repaint old feathers. A feather is dead tissue, like a fingernail, so a bird changes color only by dropping feathers and growing new ones. This process is called molting.

Most songbirds molt once a year, after the breeding season. The American goldfinch is unusual: it is the only member of its finch subfamily known to have two molts every year.

• Fall molt (late summer to fall): after the young have left the nest, goldfinches replace all their feathers, including the wing and tail feathers. The new body feathers are dull olive-brown, buff and gray.
• Spring molt (late winter to spring): goldfinches replace their body feathers but keep their wing and tail feathers. In males, the new body feathers are bright lemon-yellow, and a black cap grows on the forehead.

Because the spring molt happens gradually over several weeks, birds at feeders in March and April often look blotchy, with patches of yellow and olive. By late spring, males are fully bright. The exact timing varies with latitude and weather, so goldfinches in the South usually brighten earlier than birds in Canada.

Why is the male so bright in summer?

Bright color in birds is usually about attracting a mate and warning off rivals. The male’s yellow plumage and the female’s choice go together: research on American goldfinches suggests that females prefer brighter, more colorful males, and that color can signal a male’s health and condition.

The yellow comes from carotenoids, natural pigments in plants. Goldfinches cannot make carotenoids themselves; they get them from the seeds and plant foods they eat and deposit them in the growing feathers. A well-fed, healthy male can build more of these pigments into his feathers, so a brilliant coat can be an honest sign of quality.

The bill changes too. In spring, the bills of both males and females turn bright orange, then fade to a dull pinkish color later in the year.

Why turn dull in winter?

Scientists do not know every reason, but there are several likely benefits:

• Less attention from predators. A dull olive-brown bird is harder for hawks to spot than a bright yellow one, which matters when goldfinches spend the winter feeding in open fields and at feeders.
• No need to show off. Goldfinches do not hold breeding territories in winter. Without courtship, there is little benefit to costly bright colors.
• Fresh, warm feathers. The complete fall molt gives each bird a full new set of feathers, including wing and tail feathers, before winter weather sets in.

Molting takes energy and protein, so it happens when food is available and when the birds are not busy raising young. Goldfinches nest very late in summer, so their fall molt comes after nesting is finished, as explained in why goldfinches nest so late.

Males, females and young birds compared

The difference between the sexes is greatest in summer.

In winter the two sexes look much alike, but males can usually be told by their blacker wings and the yellow patch at the shoulder.

Do other goldfinches change color?

The seasonal color change is a special feature of the American goldfinch. Its relatives behave differently:

• The European goldfinch (Carduelis carduelis) keeps its red face and golden wing bars all year. Its colors look slightly duller only as feathers wear.
• The lesser goldfinch of the western United States and Mexico looks much the same all year, so males stay yellow below with a dark back even in winter.

Many other North American birds change between breeding and nonbreeding plumages, including scarlet tanagers and many warblers, but the American goldfinch is one of the most familiar examples at backyard feeders.

A state bird that changes its colors

The bright summer male is the image people know best, and it explains why the American goldfinch was chosen as the state bird of Iowa, New Jersey and Washington. Yet anyone who watches a feeder all year sees two quite different birds: the shining yellow songster of summer and the quiet olive-brown visitor of winter. Both are the same species, and both are in the full list of US state birds.