The other day I was debating whether the new Backyard Birds I was seeing were Pine Warblers or American Goldfinches. I settled on the bird being a Pine Warbler.
I finally figured out how to tell the difference between a Pine Warbler and an American Goldfinch.
The beak on the Pine Warbler (above) is a bit more narrow and long compared to the American Goldfinch (below). Also, and most telling, the Pine Warbler has yellow running down the breast, whereas the American Goldfinch just has yellow around the head and neck.