The swamp harrier (also known as marsh harrier) is largely dark brown, becoming lighter with age. It hunts by flying slowly, low to the ground, on upswept wings. The body length is 50cm to 58cm, tail about half, wingspan is 120cm to 145cm. The recorded weights of adults range from 580g to 1100g, and females are significantly larger than the males.
This species nests on the ground, often in swamps, on a mound in reeds or other dense vegetation. The clutch size may range from 2 to 7, but is usually 3-4, dull white with pale blue or pink tinge. The incubation period is about 33 days, with chicks fledging about 45 days after hatching. Breeding season September to January.
Solitary. Can be sedentary or nomadic. Sometimes disappears from some areas when not breeding. Migrates from Tasmania to mainland Australia. The voice is a short harsh scream and high-pitched single whistle. The swamp harrier is widespread throughout Australasia and the South Pacific, except in arid regions. It is the commonest raptor in New Zealand. It is mainly found in coastal areas, in swampy grasslands and reed beds, rarely far from water.
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.