The American Goldfinch is mostly monogamous, but a number of females switch mates after producing a first brood. The first male takes care of the fledglings while the female goes off to start another brood with a different male.
--Cornell Lab of Ornithology
I don't have any comment about that. I just thought I'd throw it out there.
Goldfinches are plentiful birds and fun to take pictures of because their plumage varies from season to season so you can often get them in various forms of molt.
The picture shown is of one male screeching at the other. Below is a male and female, with the female in flight