2007, Irene M. Pepperberg, “19: Emergence of Linguistic Communicetion”, in Caroline Lyon, Chrystopher L. Nehaniv, Angelo Cangelosi, editors, Emergence of Communication and Language, page 376
2011, F. Keith Barker, “Phylogeny and Diversification of Modern Passerines”, in Gareth Dyke, Gary Kaiser, editors, Living Dinosaurs: The Evolutionary History of Modern Birds, page 244