You will need:

Mesh bag – an old onion or orange bag would work or a small mesh laundry bag.

Bright pieces of yarn 2 - 3 inches in length

What you do:

1. Fill the bag with the pieces of yarn, lint, or cotton batting.
    

2. Pull some pieces through the mesh so the hang out and are easily seen.
    

3. Hang in a tree or off of your porch. Now watch the birds come and take the string to build their nests.
    

4. Later take a walk around your neighborhood and see of you can spot some nests that have been made with your string.