Tree Swallows Tachycineta bicolor, who line their nests with found feathers, fledged their five young out of the nestbox a few days ago. This is what I found when clearing out the box. I clean and save such feathers, then put them out again in Springtime for the next nesting season. Some birds place colored or shiny items in their nest . . . wire, yarn, ribbons, etc.
This collection included a little blue sparkly hair pin!