I tentatively call it White-backed to separate it from the images of Black-necked Stilts.
It shows a lot of white on the head and an almost complete white band across the lower neck like White-backed Stilt.
However, there is a lot of individual variation within Black-necked Stilt and possible hybrids as well.
Feel free to comment on this bird. One White-backed Stilt has been claimed in El Oro, Ecuador a few years ago.