Goldfinches can be best described as flighty. They're at your feeder one day and gone the next. They also change their brilliant coat and colors twice a year. In the summer the male Goldfinch is bright yellow with the female being a bit paler. Come October they start molting out of those colors into a drabber frock. In the winter you can tell the Goldfinches at your feeders by the strong black and white wing bars.
Goldfinches are also the last bird to nest in your yard. Usually they start nesting in late July with their molted young appearing late August or early September. Goldfinches are actually considered vegetarians in one respect. Unlike most species of birds Goldfinches don't eat insects. They eat seed and seed alone. In fact they will also feed their young globules of spit and seed.
Goldfinches eat Nyjer seed or Finch Mix from Wild Birds Unlimited but can also eat sunflower seeds. In fact if you grow sunflowers in your yard you can expect a charm of Goldfinches. They also like Cone Flowers.
Nyjer is not Thistle and Thistle is not Nyjer!
Guizotia abyssinica or Nyjer is an erect, stout, branched annual herb, grown for its edible oil and seed. Native to Eithiopia and Malawi, nyjer seeds are also grown in India.
Commercial nyjer seed is grown in Africa, India and other areas of southeast Asia, and the seed is imported around the world as a popular type of birdseed.
Before it is imported, however, nyjer seed is sterilized by intense heat to prevent germination of any additional seeds that may be part of the mix. Treated nyjer seed may germinate but would typically be stunted, limiting its spread and offering less of a threat to native plants.