This is also a good way to get one for your life list without even trying!
I first discovered this when a flock of winter Goldfinches descended upon my feeder a few years ago. They loved that feeder and I got used to seeing them there until one day a bright yellow bird, not a Goldfinch, mind you, was found among them.
Come to find out Pine Warblers like to travel with winter Goldfinches!
Just recently while going through my old birding photos, I came across this bird that as an inexperienced birder I had passed over as a winter Goldfinch. I had just heard through the wire that Pine Siskins were seen in backyards traveling with the Goldfinches. And what do you know?
Pine Siskin Serendipity.