Pyle, Peter (1997). Identification guide to North American birds : a compendium of information on identifying, ageing, and sexing "near-passerines" and passerines in the hand. Steve N. G. Howell, Siobhan Ruck, Institute for Bird Populations, Point Reyes Bird Observatory. Bolinas, Calif.: Slate Creek Press. ISBN0-9618940-2-4. OCLC38593534.