Nesting Material Refill for Wreaths and more! Use this nest builder refill kit for the nesting wreath or birdie bell. The only nesting material available that contains a mixture of five natural-colored materials preferred by North American birds! Feathers, string, cotton, hemp and aspen fiber are all included. Encourages birds to nest in your yard, and allows more bird watching opportunities as birds return again and again to choose their favorite nest materials.