Quiz question: Name a bright yellow bird, one that seems invariably chipper, has an unusual diet, moves around in flocks of its own kind and lives among us in disguise all winter.

If “male American goldfinch” sprang to mind, then you know this small, peppy bird that flocks to seed feeders and stands of flowering plants and fills the skies with its ebullient sounds.

In summer walks through open areas with prairie plants swaying in a breeze I often encounter flocks of these small yellow finches feeding busily on seed heads (females are a less vibrant, taupe-y color). As they erupt into flight, scattering in all directions, they stay in touch with each other by singing a call sounding remarkably like “po-ta-to chip,” repeated over and over. Their undulating flight is fun to watch, too.

Fall must be goldfinches’ favorite season, since it’s the time when plants go to seed, in fields, roadsides, rain gardens and our home gardens. In fact, unusual in the bird world, the goldfinch menu lists only one item — seeds — and there’s no room for insects or any other food in their diet. Where nearly all other songbirds raise their broods on a diet dominated by insects, goldfinch nestlings grow big and strong on a slurry of parental saliva and smashed seeds.

A young finch eyes some seeds. (Lew Troast Jr.)

Many of us who maintain backyard feeders believe that summer’s goldfinches migrate away in the fall. Feeders once jammed with yellow birds at every port now only host sparrows, they report. But a closer look at those “sparrows” reveals some unsparrow-like features, such as a conical beak coming to a sharp point, and dramatic markings on folded wings. These are goldfinches in their winter garb, with males trading their yellow feathers for a less-conspicuous brown and taupe coat, resembling females of the species. This helps them avoid predators in winter.

Late in the winter, the males will start molting into their flashy yellow plumage for the breeding season. The change is so dramatic between summer and winter that it’s easy to see how some folks think their finches disappear.

But just to complicate matters, it should be mentioned that many goldfinches do migrate, spending winters in the southeastern U.S. or northern Mexico. We still see some gathering at our feeders and these either are birds from farther north dropping down for the season or resident birds that don’t migrate.

A goldfinch in winter plumage. ( Don Severson)

It’s nice to read in the Minnesota Breeding Bird Atlas that goldfinch populations are stable in our state and it’s fun to note that this scientifically oriented tome refers to goldfinches as “joyful, high-spirited birds.”

They brighten our summers, and once you learn to recognize them in their winter disguise, they perk up the winter landscape, too.

St. Paul resident Val Cunningham, who volunteers with the Audubon Society and writes about nature for several publications, can be reached at valwrites@comcast.net.