Ridgway 1914. The birds of North and Middle America. Part 6. Picidae, Capitonidae, Ramphastidae, Bucconidae, Galbulidae, Alcedinidae, Todidae, Momotidae, Caprimulgidae, Nyctibiidae, Tytonidae, Bubonidae. Washington DC Smithsonian Institution U S National Museum Bulletin, No. 50(Pt. 6) 1914: (i-xx 1-882)