Unlike the hybrids, these birds show an all white foreneck and isolated black nape. Females have slightly longer, more upturned bills than males and duller, less shiny black. I believe this is a female. This species is often called the White-headed Stilt (e.g. IOC). The name Pied Stilt was adopted by Clements starting with the 6th edition. This species arrived in New Zealand from Australia in the 19th century and increased through the mid 20th century, but now appears to be declining.
Taxonomy and geographic variation controversial. H&M4 and HBW lump this bird with the Black-necked Stilt of the Americas, the White-backed Stilt of South America and the Black-winged Stilt of Eurasia and Africa. To make matters more confusing OSNZ uses the name Pied Stilt for this entire assemblage. Meanwhile Clements and the IOC split the entire group into four species. If we follow the lumpers, this bird is H. h. leucocephalus, which ranges from Australasia to Philippines through Indonesia. If we follow the splitters, then this species is monotypic. Digiscoped with Panasonic DMC-LX5 | Nikon FS 3 | 30XWA | hand-held, no adapter.
References:
Adams, R. 2013. Pied stilt. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz
Marchant, S.; Higgins, P.J. (eds) 1993. Handbook of Australian, New Zealand and Antarctic birds. Vol. 2, raptors to lapwings. Oxford University Press, Melbourne.
Pierce, R.J., Kirwan, G.M. & Boesman, P. (2017). 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 http://www.hbw.com/node/53759 on 21 March 2017).