Theristicus is a genus of birds in the Threskiornithidae family. They are found in open, grassy habitats in South America. All have a long, decurved dark bill, relatively short reddish legs that do no extend beyond the tail in flight (unlike e.g. Eudocimus and Plegadis), and at least the back is grey.
Formerly, T. caudatus included T. melanopis as a subspecies, but today all major authorities accept the split. Furthermore, it has recently been suggested that the taxonbranickii should be considered a species, but at present most authorities maintain it as a subspecies of T. melanopis.
Matheu, E., & J. del Hoyo (1992). Family Threskiornithidae (Ibises and Spoonbills). pp. 472–506 in: del Hoyo, J., A. Elliott, & J. Sargatal (editors). Handbook of the Birds of the World. Vol. 1. Ostrich to Ducks. Lynx Edicions, Barcelona. ISBN 84-87334-10-5