This Pine Siskin allowed me to approach the edge of the feeder without the slightest concern. I'm thinking it was a pretty recent fledgling. It was much plumper than the adult Pine Siskins, which is a common attribute of fledglings among many types of birds. Their parents just spent all their stores of fat migrating, incubating, and feeding their chicks. So, the chicks often look huge next to their exhausted parents. The other less scientific reason I am confident this is a young Pine Siskin - look at all the food on its face!
Check out the bill deformity on this female Lesser Goldfinch! A little cross-bill action with a sword for a bottom lip.