Recently I drove up the Thames coast Coromandel and at Te Puru beach 100's of oyster catcher birds were waiting along the water’s edge. These are a pretty bird with lovely white bellys I have only ever seen them in pairs.
The Oyster Catcher was previously shot for food until 1922 when they were protected due to low numbers. They are long-lived, with some birds reaching 30+ years of age. Adults show high fidelity to mate and many breeding pairs remain on territory year-round, but some join flocks of pre-breeders for the autumn and early winter, typically at larger estuaries.
I suspect these birds are a pre breeding flock since it is late summer here.