Ithaca hair! Love it. When we had our dairy goats they would rub against the fence to shed their coat and the birds would take the hair. Somewhere I have a pic of a chickadee nest in a box and it was a work of art, the white hairs woven in with green moss.
I have four fallen nests from Wrens and other small songbirds, and two have hair from my Black Lab woven into them. The other two I found our here at the ‘new’ farm and they have Ithaca tail and mane hair in them.
Nature wastes nothing! :)