Marsh Harriers are birds of prey in the harrier subfamily Circus. They are medium-sized raptors and the largest and broadest-winged of all harriers. All breed in dense reedbeds.
Most authorities recognize three separate but closely related species:
- Western Marsh Harrier (Circus aeruginosus)
- Eastern Marsh Harrier (C. spilonotus
- Swamp Harrier (C. approximans)
They were once thought to be a single species with an almost worldwide range (excluding only the Americas), and three subspecies: the western (C. aeruginosus aeruginosus), eastern (C. aeruginosus spilonotus), and the Australasian-Pacific were considered variant.
The Western Marsh Harrier (Circus aeruginosus), often simply called the Marsh Harrier, breeds extensively across Europe and Asia. It is migratory except in the mildest regions, and winters mainly in Africa.
The Western Marsh Harrier is a typical harrier with long wings held in a shallow V in its low flight. Also, it is similar to other harriers in having distinct male and female plumages, but its plumages are quite different from those of its relatives.
The male has wings with grey and brown sections and black wingtips. Its head, tail and underparts are greyish, except for its chestnut belly.
The female is mainly brown with a cream-colored crown and cream leading edge to her wings.
Marsh Harriers prey on small mammals, insects and birds, surprising them as they drift low over fields and reedbeds.
The Eastern Marsh Harrier (C. spilonotus) can be found in the grasslands and wetlands of southern Siberia, northern Mongolia, north-east China, Manchuria and Japan. It migrates in winter to South-east Asia, the Philippines and northern Borneo.
Like all marsh harriers it prefers open, wet environments, and is frequently seen drifting low over rice fields, interspersing long, circling glides with two or three slow, powerful wingbeats. Two subspecies are recognized: C. spilonotus spilonotus of east Asia, and C. spilonotus spilothorax, of New Guinea and the islands nearby (which was previously thought to be a separate species and is still often called the Papuan Harrier).
The Swamp Harrier (C. approximans) is somewhat larger than C. spolonotis at about 50 to 58 cm. It is also a little darker, and has less heavily barred wings and tail. It is commonly found in suitable habitat anywhere in Australasia, particularly in the higher rainfall areas to the east, south-east, and south-west, of Australia and throughout New Zealand, but also in the tropical north of Australia, and the island groups to the east of the Coral Sea, New Caledonia and Vanuatu. It sometimes used to be known as the Australasian Harrier.