Reference

Michael P. Stuart Irwin (1975): Adaptive morphology in the Black and Slatey Egrets Egretta ardesiaca and Egretta vinaceigula, and relationships within the genus Egretta (Aves: Ardeidae) – Bonn zoological Bulletin - früher Bonner Zoologische Beiträge. – 26: 155 - 163.