If you have small amounts of leftover yarn, stuffing, or fabric, the birds might have a use for them. After reading many birders' forums, I've distilled these guidelines:
- Use natural fibers only.
- Cut yarn into pieces no longer than 6 inches (to avoid tangled-up birds).
- Cut fabric into strips no larger than 1/2 by 6 inches.
- Lay your offerings out on bushes and trees, or put them in a meshy hanging container such as a suet cage.
Note that dryer lint is not recommended. If the nest never got wet it might be fine, but it retains water a long time (leading to cold nests) and is crumbly after drying. Instead, use lint to stuff pincushions, or make it into art.
If you want more nesting-promotion advice without wading through forums, visit the National Wildlife Federation and All About Birds.