These 6″ bird nest balls are made with grapevine and filled with alpaca fiber. The fiber is soft and warm, so it will help keep the local birds nests comfy and warm for their eggs and babies. Each nesting ball comes with a jute twine string for you to tie on a hook or a branch. If you have bird feeders, it’s recommended to place the nesting balls near the feeders. These grapevine balls are refillable too!