Hogstad, Olav. 2008. “Sexual Bill Dimorphism Supports Separation of the Woodpecker Genera Dendrocopos Koch (1816) in the Palaearctic and Picoides Lacépède (1799) in the Nearctic”. Ornis Norvegica 31 (January), 183-88. https://doi.org/10.15845/on.v31i0.167.