The Western Marsh Harrier is a mid-sized bird of prey from temperate and subtropical western Eurasia and adjacent Africa. It is also known as the Eurasian Marsh-harrier. A species of the harrier genus Circus, its scientific name is Circus aeruginosus.
Formerly, a number of relatives were included in C. aeruginosus, which was then known as “Marsh Harrier“. The related taxa are now generally considered to be separate species: the Eastern Marsh-harrier (C. spilonotus) and the possibly distinct Papuan Harrier (C. (s.) spilothorax) of eastern Asia and the Wallacea, the Swamp Harrier (C. approximans) of Australasia and the Madagascar Marsh-harrier (C. maillardi) of the western Indian Ocean islands.
The Western Marsh Harrier is often divided into two subspecies:
- Tthe widely migratory C. a. aeruginosus which is found across most of its range, and
- C. a. harterti which is resident all-year in north-west Africa.
The Western Marsh Harrier is 42 to 56 cm in length, and has a wingspan of 115 to 140 cm. It is a large, bulky harrier with fairly broad wings, and has a strong and peculiar sexual dichromatism.
The male‘s plumage is mostly a cryptic reddish-brown with lighter yellowish streaks, which are particularly prominent on the breast. The head and shoulders are mostly pale greyish-yellowish. The rectrices (the long flight feathers of the tail) and the secondary and tertiary remiges (flight feathers of the wing) are pure grey, the latter contrasting with the brown forewing and the black primary remiges at the wingtips. The upperside and underside of the wing look similar, though the brown is lighter on the underwing. Whether from the side or below, flying males appear characteristically three-colored brown-grey-black. The legs, feet, irides and the cere of the black bill are yellow.
The female is almost entirely chocolate-brown. The top of the head, the throat and the shoulders have of a conspicuously lighter yellowish colour; this can be clearly delimited and very contrasting, or (particularly in worn plumage) be more washed-out, resembling the male’s head colors. But the eye area of the female is always darker, making the light eye stand out, while the male’s head is altogether not very contrastingly colored and the female lacks the grey wing-patch and tail. Juveniles are similar to females, but usually have less yellow, particularly on the shoulders.
There is a rare hypermelanic morph (genetic mutation) with largely dark plumage. (Please refer to the below image.) It is most often found in the east of the species’ range.
Juveniles of this morph may look entirely black in flight.
Distribution and ecology
This species has a wide breeding range from Europe and northwestern Africa to Central Asia and the northern parts of the Middle East. It breeds in almost every country of Europe but is absent from mountainous regions and subarctic Scandinavia. It is rare in the British Isles and does not currently breed in Ireland or Wales. In the Middle East there are populations in Turkey, Iraq and Iran, while in Central Asia the range extends eastwards as far as north-west China, Mongolia and the Lake Baikal region of Siberia.
Most populations of the Western Marsh Harrier are migratory or dispersive. Some birds winter in milder regions of southern and western Europe, while others migrate to the Sahel, Nile basin and Great Lakes region in Africa, or to Arabia, the Indian subcontinent and Myanmar. The all-year resident subspecies harterti inhabits Morocco, Algeria and Tunisia.
Vagrants have reached Iceland, the Azores, Malaysia and Sumatra. The first documented (but unconfirmed) record for the Americas was one bird reportedly photographed on December 4, 1994 at Chincoteague National Wildlife Refuge in Accomack County, Virginia (USA). Subsequently, there were confirmed records from Guadeloupe (winter of 2002/2003) and from Laguna Cartagena National Wildlife Refuge on Puerto Rico (early 2004 and January/February 2006).
Like the other marsh-harriers, it is strongly associated with wetland areas, especially those rich in Common Reed (Phragmites australis).
It can also be met with in a variety of other open habitats, such as farmland and grassland, particularly where these border marshland.
It is a territorial bird in the breeding season, and even in winter it seems less social than other harriers, which often gather in large flocks. But this is probably simply due to habitat preferences, as the marsh-harriers are completely allopatric while several of C. aeruginosus grassland and steppe relatives winter in the same regions and assemble at food sources such as locust outbreaks. Still, in Keoladeo National Park of Rajasthan (India) around 100 Eurasian Marsh Harriers are observed to roost together each November/December; they assemble in tall grassland dominated by Desmostachya bipinnata and Vetiver (Chrysopogon zizanioides), but where this is too disturbed by human activity they will use floating carpets of Common Water Hyacinth (Eichhornia crassipes) instead – the choice of such roost sites may be to give early warning of predators, which will conspicuously rustle through the plants if they try to sneak upon the resting birds.
Diet / Feeding
It hunts in typical harrier fashion, gliding low over flat open ground on its search for prey, with its wings held in a shallow V-shape and often with dangling legs. It feeds particularly on small mammals such as water voles (Arvicola) and birds such as Acrocephalidae warblers, but also eats insects, squamates, amphibians, fish and carrion.
The start of the breeding season varies from mid-March to early May. Western Marsh Harrier males often pair with two and occasionally three females. Pair bonds usually last for a single breeding season, but some pairs remain together for several years.
The ground nest is made of sticks, reeds and grasses. It is usually built in a reedbed, but the species will also nest in arable fields. There are between three and eight eggs in a normal clutch. The eggs are oval in shape and white in colour, with a bluish or greenish tinge when recently laid. The eggs are incubated for 31–38 days and the young birds fledge after 35–40 days.
Status and conservation
The Western Marsh Harrier declined in many areas between the 19th and the late 20th century due to persecution, habitat destruction and excessive pesticide use. It is a now a protected species in many countries. Its numbers are rising again in many places, most notably perhaps in Great Britain, where a single breeding female was left in 1971, whereas today over 200 pairs are present.
It still faces a number of threats, including the shooting of birds migrating through the Mediterranean region. They are vulnerable to disturbance during the breeding season and also liable to lead shot poisoning. Still, the threats to this bird have been largely averted and it is today classified as Species of Least Concern by the IUCN.
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