They are the American Goldfinch. These photos are from Wikipedia. I have never been good at taking photos of birds on my bird feeder. They always get frightened and fly away before I can get a good picture!
These birds are special to me because I always looked foward to seeing them in the Spring when we lived in Atlanta. Every Spring, they would come and feed on the buds of the tree that was right outside the bay window in my living room! It wouldn't just be a couple of them, either. There would be a whole FLOCK of them! Their color was more dull than these pictured above.
I don't think I have ever seen Goldfinch's in the summertime. Their yellow body is MUCH more vibriant in the summer! They are beautiful!! I only saw a male & a female this morning, but I was thrilled!!