Kelp Gull
Larus dominicanus

Kelp Gulls are the largest of the three gull species in New Zealand. They occur from southern South America through to Australia as well as having a different subspecies in southern Africa (although this sometimes split as a seperate species). As with other large gulls, they can be agrressive and have even been found to attack surfacing whales for their blubber by pecking through the skin. They are known in New Zealand as the Black-backed Gull and by the Maori as the Karoro.
The first two are adults, the third is a third-year bird and the last is a juvenile.