Formerly treated as a separate species called "Hawaiian Stilt," but now lumped with the Black-necked Stilt. It differs from nominate H. m. mexicanus on the continent in that adults have more extensive black on the face and neck. This race also averages larger with longer bill and legs. The browner backed bird in the foreground is a female. Some authors consider both to be races of the Black-winged Stilt (H. himantopus). Like most native Hawaiian waterbirds it is endangered with a total population of 1,500 to 1,800 birds of which only 125-350 survive on Kauai. Canon PowerShot SX60 HS.
References:
Chandler, R. (2009). Shorebirds of North America, Europe, and Asia: A photographic guide. Princeton.
Pierce, R.J. & Kirwan, G.M. (2020). Black-winged Stilt (Himantopus himantopus). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from https://www.hbw.com/node/53759 on 30 January 2020).
Robinson, J. A., J. M. Reed, J. P. Skorupa, and L. W. Oring (1999). Black-necked Stilt (Himantopus mexicanus), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.449