Sure, you could save your pet's hair, shred old washcloths and gather other odds and ends to provide nesting materials for your birds (don't use dryer lint, the fragrance and static cling residues aren't good for your birds). Or, you could simply click and purchase this refill for your Bird Nester box!
Goldfinches don't nest until thistle down is available, which usually is late July/early August, so be sure to keep your Bird Nester full all summer long.