Tuesday, December 4, 2007

Common Feeder Birds: American Goldfinch

Summer male American Goldfinch

Wild canaries! That was what my family called them when I was a kid. I later learned their more widely used name of American Goldfinch, Carduelis tristis. This beautiful little bird with the color of sunshine is always a welcome sight.

Winter female American Goldfinch

These bird are sexually dimorphic which means the males and females are different colors. In the spring/summer, the male is a vivid yellow with black cap, black wings and tail. The female is a more dull yellow-brown with olive brown wings. In the fall, the males lose their bright yellow hue and look almost the same as the female, except for their yellow shoulder patch. The females also go through this molt in the fall, but it just results in a duller look. Goldfinch are one of the only carduelis finches to go through a molt in both the spring and the fall. In the spring molt, American Goldfinches only molt their body feathers while in the fall molt they lose body feathers as well as tail and wing feathers. Both male and female have orange bills in the spring/summer and a duller dark bill in the winter.

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.

Nesting behavior is another unique characteristic of the American Goldfinch. This is one of the few birds that nest very late in the season. American Goldfinch wait until late June to early July to nest with some of the last eggs being laid in mid-August! Some researchers believe this is timed to coincide with the abundance of food for the nestlings, since so many seed bearing plants are available then. Others believe it is for the thistle down for the lining of the nest. Since they nest so late in the season, they usually only have one brood, usually between 4-6 young.

Many of our winter visitors may be from farther north. The American Goldfinch from the north will migrate south to find food. Most Canadian populations will end up in the United States. At feeders, they enjoy black-oil sunflower seed and nyjer seed(thistle). I have seen as many as 14 American Goldfinch on one of our small thistle feeders at one time.

1 comment:

Elizabeth said...

Hi! I stumbled onto your blog while looking for pictures of male and female American Goldfinches in winter plumage. Thank you for this excellent tutorial!