That is a good question! The American Goldfinch is one of my favorite backyard songbirds because of its butterfly like flight and delicate song.
Many people don't realize that the Goldfinches are not bright yellow all year. In fact they are the only finch in North America to go through a complete molt two times a year. In the spring the male turns bright yellow with a black cap, wings, and tail, and white rump. The female keeps the duller brown color and lacks the black cap. Why?
One reason the female stays brown is that she needs to blend in with the trees when she is sitting on a nest of eggs later in the summer. Another reason is she doesn't need to be showy. The males need to be bright to attract a mate and defend their territory from other males. Research also suggests that as testosterone in male birds increases, so does the level of carotenoids, the chemicals that create the bright coloring on birds' feathers, beaks, and legs.
Many customers think that the American goldfinch disappears in the winter. Actually, in the fall, all the goldfinches molt again into their yellowish brown winter plumage. During the winter months both male and female goldfinches look similar and are actively feeding in Michigan.
Gardening Trick for Goldfinches: Habitat can be a key to attracting Goldfinches. In this case you do less work, not more. Don't worry about dandelions and don't cut off the tops of your Marigold, Zinnias, Cosmos, or Coneflowers...Goldfinches love them.
Keep the question coming to firstname.lastname@example.org