American Goldfinch winter male, photo by John Howard
Shoulder patch in winter male
American Goldfinch are closely tied to their food source. They are granivorous or eat mostly seeds. Even when they feed their young, goldfinch rely mostly on a seed diet. The Brown-headed Cowbird, which parasitize many birds nests by leaving its young to outcompete the smaller birds, does not survive in an American Goldfinch nest. The cowbird likes a diet rich in insects, which it does not get from the mother goldfinch. Most cowbird babies have retarded growth and die before they can leave the nest. Also, the males brillliant yellow hue is due to the food they ingest. Carotenoid pigments that produce yellow and orange colors in many composites or flowers in the sunflower family which is a favorite food of American Goldfinch. The frequently feed on Prairie Dock, Compass Plant, Rosinweed, and sunflowers. I used to work at a native plant nursery and we would have to put netting over these plants to keep the goldfinches from destroying the seed crops. They could wipe out a whole row of plants in no time. Besides the composites, American Goldfinch also use thistle as a food source and to line their carefully woven nests.