The swamp harrier - also known as the Australasian marsh harrier, Australasian harrier, or swamp-hawk - is a large, slim bird of prey widely distributed across Australasia. In New Zealand it is also known as the harrier hawk, or by the Māori name kāhu. Its arrival in New Zealand happened recently within the last 700 years, replacing its extinct larger New Zealand endemic sister speciesEyles's harrier. The swamp harrier belongs to the sub-family Circinae and genus Circus, which are represented worldwide, except Antarctica. The sub-family and genus are derived from the characteristic behavior of circling flight during courtship and hawking.
Description
The swamp harrier is largely dark brown, becoming lighter with age, and has a distinct white rump. It hunts by flying slowly, low to the ground, on upswept wings. The body length is, and the wingspan is 120 to 145 cm. The recorded weights of adults range from 580 to 1100 g, and females are significantly larger than the males.
Distribution and habitat
The swamp harrier is widespread through Australasia and many islands in the south-west Pacific region, including much of Australia, New Zealand, Fiji, Vanuatu, New Caledonia and as stragglers on some subantarctic islands. It is usually found in wetlands and well-watered open country. The harrier only became established in New Zealand within the last few hundred years, after lowland forests were extensively cleared by the first Polynesian settlers; it is absent from the fossil record. It has benefited from European settlement, and is now very common, especially in open farmland.
Behaviour
Common enemies of harriers are Australian magpies, masked lapwings which dive bomb and European starlings which mob individuals. They have been known to kill young kārearea and have also been heavily blamed and persecuted for killingchickens, pheasants and ducklings. Swamp harriers are the only bird of prey used for falconry in New Zealand; quarry is usually pukeko and young rabbits.
Diet
The swamp harrier mainly feeds on ground birds and waterbirds, rabbits and other small mammals, reptiles, frogs, and fish. During the winter months harriers feed to a large extent on carrion, including roadkill, frequently falling victim to vehicles themselves.
Breeding
This species nests on the ground, often in swamps, on a mound in reeds or other dense vegetation. In some districts they nest in fields of oats or barley. The clutch size may range from two to seven, but is usually three or four. The incubation period is 31 to 34 days, and is carried out by the female alone. Chicks are fed by both parents, are fully feathered by 28 days and fledging about 45 days after hatching.
