After I looked at the photos I took of this male lesser goldfinch drinking at the fountain, I realized his head was covered with pin feathers. The white keratin sheaths stand out from his black head, more noticeably on the first shot. I had never thought about other kinds of birds, besides parrots, having pin feathers after a molt, but of course they would. When a bird molts and new feathers emerge, the new feathers are covered with a keratin sheath that protects the new feather until it matures enough to slough off. One of the reason birds preen themselves and each other, is to remove the keratin sheath from their feathers.
Both shots: Focal Length 400mm, ISO 640, f/5.6, 1/125