Graves, G. R., D. F. Lane, J. P. O’neill, and T. Valqui. “A Distinctive New Subspecies of the Royal Sunangel (Aves: Trochiliformes; Heliangelus regalis) from the Cordillera Azul, Northern Peru”. Zootaxa, vol. 3002, no. 1, Aug. 2011, pp. 52–58, doi:10.11646/zootaxa.3002.1.5.