Woodpeckers are natural engineers whose abandoned nest and roost cavities facilitate a great diversity of life, including birds, mammals, invertebrates, and many fungi,moss, and lichens. Without woodpeckers, birds such as chickadees and tits, swallows ans martins, bluebirds, some flycatchers, nuthatches, wood ducks, hooded mergansers, and small owls (screech, saw-whet, and pygmy) would be homeless.