Karoro – Black Backed Gull
Larus dominicanus Black Backed, Dominican or Kelp Gull
One native bird that has greatly benefited from human settlement in New Zealand is Larus dominicanus, the black backed gull. While it is a native it is also widely distributed throughout the Southern Hemisphere from the tropics south. Given their omnivorous diet and successful breeding in the absence of predators, intelligence and aggressive behaviour the species is bound to thrive.
It is a scavenger and opportunistic feeder and takes great advantage from human agriculture, forest clearing and refuse disposal. The gull takes advantage of insects and small animals associated with farming and urban landfill. It is a coastal and inland dwelling bird, so it is a misnomer to refer to it as a ‘sea’ gull. It does certainly take advantage of what the sea throws up onto shores, including dead fish, seals and whales. It also preys on living bivalve molluscs, like other gulls, carrying shell fish to a good height and dropping them onto hard surfaces. The concrete pavements of esplanades are ideal! Eggs and young of bids such as terns are predated, and inshore or tidal fish. They do not venture far out to sea but commonly retreat to shelter in urban parks and sports fields which flood in storms and offer worms for the taking. Gulls will eat anything dead, even when putrescent, live mice, rats, birds and fast food scraps!
Given their numbers (speculated to be in the millions around N), and capacity to gather at airports and risk bird strike to aircraft, they are not only unprotected under wildlife law, but are also actively subject to population control. There are large colonies on offshore islands such as Kapiti, Mana and Matiu-Somes, locally, and smaller colonies at places such as Taputeranga Island. Where gull numbers build up to be a nuisance, as at some landfills and around airfields, control is attempted using poisons, egg pricking, or egg ‘smothering’ by coating eggs with oil. (While the adults think the eggs are viable they will not re-lay further clutches.)
Karoro were recognised by Māori people as a useful predator of the caterpillars and grubs which threatened kumara crops, and birds would accompany them on food gathering expeditions for the sake of the scraps. Some birds may have been tamed or had their wings clipped so as to stay around for crop pest control.
Gulls breed in colonies (for mutual protection) on a wide variety of sites – dunes, rocky headlands, boulder banks, even up to 1000-1500m asl. Nests are generally an untidy stack of dry grass and sticks, seaweed and feathers, with a depressed centre for the eggs. Eggs incubate for up to a month, then the chicks fledge at about 2 months. They are mature to start breeding themselves at age 4 and can live to 9 or even up to 18 years.
Heather, B., & Robertson, H., Field Guide to the Birds of New Zealand, 2000. Oliver, W.R.B., New Zealand Birds, 1955.
Best, Elsdon, Forest Lore of the Maori, 1942.
Te AraPhotos: MH