I've been ignorant about pine siskins until now. I have known the name, and had a vague idea of what they looked like, but never delved into learning more about them.
I've had goldfinches as my feeders for years. Now I come to find out that I've probably had pine siskins as well. I certainly have them this year.
Both kinds of birds are in the finch family, and they often flock together. Siskins will have irruptions, which means that some years there will be many, many more than in other years. I suspect that what has happened is that this is an irruption year, and so I have finally noticed them.
Goldfinches and pine siskins are about the same size and shape, and look vaguely similar in their winter plumage, though not really, if you know what you are looking for. Goldfinches are not very gold in the wintertime, but they are mostly solid colored, with black and white stripey wings. Siskins are more brown, and are unmistakeably streaky all over. A non-breeding female goldfinch could be mistaken for a male pine siskin - and apparently I've been doing just that for quite some time!
Well, as my father used to say, "You learn something new every day."
More info on Pine Siskins
More info on Goldfinches
(and I just figured out how to label a link without actually putting the url in the text!)