There are dozens of types of bird netting on the market designed for keeping different bird species from nesting on balconies. Most netting costs are based on the mesh size, durability of the material, and the visibility of the netting itself. The thickness of the mesh or rope should be at least four millimetres. Sizing depends on the bird species it is targeting as areas with larger gulls and crows require a heavy-duty measurement of at least four inches. Medium-sized birds such as pigeons can be kept away with a mesh netting of two inches, while smaller birds only require ¾-inch to 1 1/8” netting.