The glitter of gold

They look like little pats of butter flying through the air, dipping and rising as though on an invisible roller coaster. There's something cheerful about Goldfinches. You can't see one without smiling.
We've had a lot at our feeder in the past two weeks. Goldfinches are year-round residents of the South. In winter, they're joined by Goldfinches from the north drawn by the warmer climate. What makes them gold? The carotenoid pigments in the seed they eat.
They perch in a water oak tree in the back yard, and seem to float down to the feeder, like a yellow leaf caught by a breeze.