Frank B. Gill (6 October 2006). Ornithology. Macmillan. pp. 414–. ISBN978-0-7167-4983-7. Archived from the original on 7 January 2014. Retrieved 5 December 2012.
Frank B. Gill (6 October 2006). Ornithology. Macmillan. pp. 414–. ISBN978-0-7167-4983-7. Archived from the original on 7 January 2014. Retrieved 5 December 2012.