American Goldfinches are almost exclusively granivorous (consumers of seeds/grains). Very few insects are consumed by these birds, even when feeding nestlings. This is highly unusual in that spiders and insects are an essential part of 96% of N.A. terrestrial bird species. At the very least, most seed-eating birds feed their nestlings insects. (Brown-headed Cowbirds lay their eggs in other birds’ nests, leaving the raising of their young up to the host bird. It is rare that a cowbird chick will survive to leave an American Goldfinch nest, probably because it cannot thrive on a diet of virtually all seeds.)
The seeds of plants in the Composite family (sunflowers, thistles, dandelions, etc.) are the preferred food of goldfinches. Thistle seeds, being high in fat and protein, are high on the list. There appears to be a correlation between the late nesting period of goldfinches (late June or early July) and the flowering of thistles. By the time American Goldfinch eggs have hatched, there is an ample supply of thistle seed for the nestlings.
Now is the time to keep an eye on the seedheads of thistles, dandelions and other composites for the acrobatic seed-plucking antics of American Goldfinches.
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