Black-backed gulls.
Black-backed gulls or karoro (Larus dominicanus) can be found in the southern hemisphere from Antarctica to the subtropics. Elsewhere they are known as Dominican or kelp gulls. The subspecies in New Zealand is the widespread Larus dominicanus dominicanus. There are probably over two million in coastal and near-shore environments, and inland waterways. They do not generally venture far out to sea.
Of New Zealand’s gull species, black-blacked gulls are the largest, at 60 centimetres long. Males weigh over 1 kilogram, and females about 850 grams. Adults have white bodies, black wings, and yellow bills and legs. Original public domain image from Flickr