Karoro - black-backed gull - Larus dominicanus
This karoro chick and its nest were in a spectacular spot, high on top of a large log of driftwood in the middle of an expanse of tidal mudflats. At about the shoulder height of an average man, the nest was far higher above the tide and flood line than neighbouring nests on the tidal banks which were less than a metre above the high tide mark and well within reach of a flood. But the river nesting birds of NZ know the weather and while sometimes a flood takes out nests or chicks, most calculate the gamble correctly and raise chicks successfully during the summer dry while the river remains low.
Other common names: — Southern black–backed gull, dominican gull, kelp gull, laughing gull. 60 cm., males, 1050g., females 850g., wingspan, 120cm. In the adult, the head, neck, underparts, rump and tail are white, the back and upper wings are black with a narrow white trailing edge; the bill is yellow with a red spot at the tip of the lower bill; the eye is pale yellow and the legs greenish yellow; juveniles are brown; in the second year the back is brown and the breast and neck are white flecked with brown; voice of young is a shrill whistle.
Robust, intelligent, opportunistic and aggressive, the black-backed gull is the only large gull in New Zealand. One of the most common and conspicuous birds of our coasts.
The black-backed gull is a circumpolar navigator, living in and around the coasts of South America, South Africa, south–east Australia and New Zealand. Being a scavenger by nature, it lives and breeds in a multitude of places, from rocky ledges to open areas of pasture. vetula breeds in South Africa and dominicanus breeds widely in the subantarctic and temperate southern hemisphere.
Unlike most of our native bird life, the black–backed gull has adapted well to European settlement, from taking advantage of an abundant supply of insects and small animals off pasturelands to scavenging off refuse tips in the urban environment and foraging along the coastal front.
Every kind of animal matter cast up by the waves is greedily devoured, whether fresh or putrified, including the carcasses of whales and seals, dead fish and birds. It feeds largely on bivalve molluscs, breaking the shell by carrying it to some height and dropping it on hard sand or on rock. It also feeds on the eggs and young of birds, especially the terns near which it breeds; and on adult birds it is able to catch; and on grubs and worms which it finds on its inland excursions. Small fishes are caught, sometimes from the surface of the sea and sometimes from tidal pools.”
On farms they invariably turn up at lambing and at calving time to take advantage of dropped afterbirth and any weak or dead animals. Oliver also records the destruction of large numbers of tuatara on Stephen's Island; "a gull waits at a burrow for hours until a tuatara emerges, grabs it and then flies to sea and back to its nest, dropping the lizard every now and then to kill it."
Occasionally, the Karoro sea gull was tamed by Maori and employed as a pest–destroyer, released among the kumara (sweet potato) crops that they might consume the the big caterpillars that infested the plants.