The downy seed from a Thistle provides nest material for Goldfinches. They do not nest until the Thistle has flowered and seeded out.
We have a few Goldfinches. They visit the Thistle ( Niger Thistle Seed) feeder and the bird bath. Niger Thistle Seed is heat treated so it is a sterile seed… it won’t produce thistle plants in your yard.
Here is one pair a male on the left and his dowdy female partner on the right. I hope we see little finches soon.