We have quite a few yellow finches. They start to nest in late July when the flowers set seeds. They favor black eyed susans and Echinacea types. We also have purple finches, but I haven't seen them take the nesting fluff yet.
This morning we have a little female taking nesting materials.
I have an inexpensive corn cob holder for winter for the squirrels.
In spring I stop feeding them, and I put in nesting cotton fluff for the birds.
I do this mostly for the hummingbirds, which hubby saw this morning taking the fluff as well. But other birds take it too.
Oh my, she is back for a second load. She is really taking ALOT or it is another female. Big beak fulls. It is getting pretty decimated!

I'll have to put some more out!
This is what it looks like:
http://www.ebay.com/itm/Corn-Cob-Fee...item3ca223581a
WalMart and Lowe's typically have these too...they are so inexpensive. A friend gave me mine, and we really enjoy all the wildlife coming to it all year round!