These males fairly bubbled over with song as they enthusiastically gamboled about, singing on the wing and from perches. I kept half an eye on them as I pursued various other quarry, and was pleased when this chap alit near the top of an American Elm sapling. In between bouts of song, he would pluck elm samaras (seeds) and crunch them down.
American Goldfinches are probably the closest thing to a feathered vegan in our neck of the woods. They will opportunistically take the occasional insect, but the overwhelming majority of their diet is vegetable matter. Even the nestlings are fed a regurgitated semi-glutinous gruel of partially digested plant matter.
Even though Brown-headed Cowbirds regularly parasitize goldfinch nests, the cowbirds chicks usually perish within three days. This near 100% mortality rate is apparently due to the lack of protein in the goldfinch's plant-based diet. Cowbird chicks, and those of nearly all of our songbirds, require ample protein in the form of insect-based diets.
Not so the interesting American Goldfinch, which bucks the dominant songbird dietary paradigm.