We have American Goldfinches year around, but have many more during the winter. They are one of our most common feeder birds. When the Goldfinches start really getting into their breeding plumage in the spring, most head north.
"The goldfinch’s main natural habitats are weedy fields and floodplains, where plants such as thistles and asters are common. They’re also found in cultivated areas, roadsides, orchards, and backyards. American Goldfinches can be found at feeders any time of year, but most abundantly during winter." (From The Cornell Lab of Ornithology where there are many more photos and more information about these beautiful little bird.)
I'm not much of a birder, but I believe the top photo is a male and the bottom a female. If anyone with more experience disagrees, I'll be glad to make a correction in this post. Both birds were at the feeder hanging outside our dining nook window. Many people feed thistle seeds to Goldfinches and I'm sure the birds enjoy them, but our Goldfinches have never refused the sunflower seeds we feed.