Prevue Pet bird nesting material box. This box contains the extra nesting material you need to make your bird"s nest comfortable and cozy. Contains natural cotton thread fibers which are great for nest-building. The box easily attaches to any cage and the perforated hole pops out with a simple push so birds can have quick and easy access to the fibers. Box measures 8-1/4-inch length by 7-7/8-inch width by 5-1/8-inch height.