One of two species of this wader that occur in New Zealand, the South Island pied oystercatcher is only subspecifically different from the European bird as compared to the variable oystercatcher (Haematopus unicolor), which is a species found only in New Zealand.
The South Island pied oystercatcher breeds only in the South Island; the variable oystercatcher breeds in North, South, Stewart, and Chatham Islands.

The pied form of H. unicolor may be confused with SIPO. However the SIPO is a smaller bird and in H. unicolor he boundaries between its black and white areas are, not so precise below, and there is a mottled band on the leading edges of its underwing surfaces. Its white rump patch is only a band across the base of the tail instead of a broad wedge extending to the middle of the back, as in the South Island pied oystercatcher. And, finally, the white bars on the backs of its wings, as seen in flight, are short and narrow instead of long and broad.

In both species the sexes are very similar in appearance, except that the females are a little bigger than the males. There are differences in behaviour between the two species: the South Island pied oystercatcher breeds inland mainly on shingly river beds; the variable oystercatcher breeds on coastal sand dunes. The South Island pied oystercatcher breeds earlier than the variable and is mainly a migrant, moving to the mudflats of Auckland and Northland in winter, whereas the variable oystercatcher is predominantly sedentary.