Holy moly, I just realized, thanks to the memory jog Al's post
provided, that the odd little birds I've been noticing at my
feeders are almost certainly Pine Siskins-- little guys that look
a lot like Goldfinches -- thin bills, distinct wingbars -- except
they have thickly streaked breasts.
Hope they're there tomorrow so I can look more attentively, but
is there anything else they could be? (They're definitely not
female house finches.)