The hen harrier (Circus cyaneus) is a bird of prey. The genus name Circus is derived from Ancient Greek kirkos, meaning 'circle', referring to a bird of prey named for its circling flight. The specific cyaneus is Latin, meaning "dark-blue".
|Range of C. cyaneus Breeding summer visitor Breeding resident Winter visitor|
Falco cyaneus Linnaeus, 1766
The hen harrier is 41–52 cm (16–20 in) long with a 97–122 cm (38–48 in) wingspan. It resembles other harriers in having distinct male and female plumages. The sexes also differ in weight, with males weighing 290 to 400 g (10 to 14 oz), with an average of 350 g (12 oz), and females weighing 390 to 750 g (14 to 26 oz), with an average of 530 g (19 oz). Among standard measurements, the wing chord is 32.8 to 40.6 cm (12.9 to 16.0 in), the tail is 19.3 to 25.8 cm (7.6 to 10.2 in) and the tarsus is 7.1 to 8.9 cm (2.8 to 3.5 in). It is relatively long winged and long tailed.
The male is mainly grey above and white below except for the upper breast, which is grey like the upperparts, and the rump, which is white; the wings are grey with black wingtips. The female is brown above with white upper tail coverts, hence females, and the similar juveniles, are often called "ringtails". Their underparts are buff streaked with brown. Immatures look like females but with less distinct barring, dark brown secondaries dark brown and less-streaked belly.
The female gives a whistled piih-eh when receiving food from the male, and her alarm call is chit-it-it-it-it-et-it. The male calls chek-chek-chek, with a more bouncing chuk-uk-uk-uk during his display flight.
This medium-sized raptor breeds on moorland, bogs, prairies, farmland coastal prairies, marshes, grasslands, swamps and other assorted open areas. A male will maintain a territory averaging 2.6 km2 (1.0 sq mi), though male territories have ranged from 1.7 to 150 km2 (0.66 to 57.92 sq mi).
These, are the one of the few raptorial birds known to practice polygyny – one male mates with several females. Up to five females have been known to mate with one male in a season. A supplementary feeding experiment on the Orkney islands showed that rates of polygyny were influenced by food levels; males provided with extra food had more breeding females than 'control' males that received no extra food.
The nest is built on the ground or on a mound of dirt or vegetation. Nests are made of sticks and are lined inside with grass and leaves. Four to eight (exceptionally 2 to 10) whitish eggs are laid. The eggs measure approximately 47 mm × 36 mm (1.9 in × 1.4 in). The eggs are incubated mostly by the female for 31 to 32 days. When incubating eggs, the female sits on the nest while the male hunts and brings food to her and the chicks. The male will help feed chicks after they hatch, but does not usually watch them for a greater period of time than around 5 minutes. The male usually passes off food to the female, which she then feeds to the young, although later the female will capture food and simply drop into the nest for her nestlings to eat. The chicks fledge at around 36 days old, though breeding maturity is not reached until 2 years in females and 3 years in males.
In winter, the hen harrier is a bird of open country, and will then roost communally, often with merlins and marsh harriers. There is now an accepted record of transatlantic vagrancy by the northern harrier, with a juvenile being recorded in Scilly, Great Britain from October 1982 to June 1983.
This is a typical harrier, which hunts on long wings held in a shallow V in its low flight during which the bird closely hugs the contours of the land below it. Northern or hen harriers hunt primarily small mammals, as do most harriers. Up to 95% of the diet comprises small mammals.However, birds are hunted with some regularity as well, especially by males. Preferred avian prey include passerines of open country (i.e. sparrows, larks, pipits), small shorebirds and the young of waterfowl and galliforms. Supplementing the diet occasionally are amphibians (especially frogs), reptiles and insects (especially orthopterans). The species has been observed to hunt bats if these are available. Larger prey, such as rabbits and adult ducks are taken sometimes and harriers have been known to subdue these by drowning them in water. Harriers hunt by surprising prey while flying low to the ground in open areas, as they drift low over fields and moors. The harriers circle an area several times listening and looking for prey. Harriers use hearing regularly to find prey, as they have exceptionally good hearing for diurnal raptors, this being the function of their owl-like facial disc. This harrier tends to be a very vocal bird while it glides over its hunting ground.
Little information is available on longevity in hen harriers. The longest-lived known bird is 16 years and 5 months. However, adults rarely live more than 8 years. Early mortality mainly results from predation. Predators of eggs and nestlings include raccoons, skunks, badgers, foxes, crows and ravens, dogs and owls. Both parents attack potential predators with alarm calls and striking with talons. Short-eared owls are natural competitors of this species that favor the same prey and habitat, as well as having a similarly broad distribution. Occasionally, both harriers and short-eared owls will harass each other until the victim drops its prey and it can be stolen, a practice known as kleptoparasitism. Most commonly, the harriers are the aggressors pirating prey from owls.
This species has a large range. There is evidence of a population decline, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e., declining more than 30% in ten years or three generations). It is therefore classified as "least concern". In the United Kingdom, however, hen harrier populations are in a critical condition, due to habitat loss and illegal killing on grouse moors. In 2012 only 617 pairs remained, representing a fall of 20% from 2004.
In some parts of Europe people believed that seeing a harrier perched on a house was a sign that three people would die. Unlike many raptors, hen harriers have historically been favorably regarded by farmers because they eat predators of quail eggs and mice that damage crops. Harriers are sometimes called "good hawks" because they pose no threat to poultry as some hawks do.
The hen harrier is a bird of open habitats such as heather moorland and extensive agriculture. However, much of its range, particularly in Ireland and parts of western Britain, has been (and continues to be) afforested, predominantly with non-native conifers such as Sitka spruce (Picea sitchensis) from North America. Hen harriers nest and forage in commercial forestry when it is young, before the canopy closes (typically at between 9–12 and years old), but do not make much use of thicket and subsequent growth stages, which typically comprise between 2⁄3 and 3⁄4 of the commercial growth cycle. Where forests replace habitats that were used by hen harriers they will therefore tend to reduce overall habitat availability. However, where afforestation takes place in areas that were previously underutilised by hen harriers, it may increase the value of such areas to this species in the long-term. Areas dominated by forestry may remain suitable to hen harriers provided that a mosaic of age classes is maintained within the forest, such that areas of young, pre-thicket forest are always available.
The Blackwater Estuary is the estuary of the River Blackwater between Maldon and West Mersea in Essex. It is a 5,538 hectare biological Site of Special Scientific Interest (SSSI). An area of 4,395 hectares is also designated a Ramsar Wetland of International Importance, and a Special Protection Area 1,099 hectares is a National Nature Reserve. Tollesbury Wick and part of Abbotts Hall Farm, both nature reserve managed by the Essex Wildlife Trust, are in the SSSI.Oysters have been harvested from the estuary for more than a thousand years and there are remains of fish weirs from the Anglo-Saxon era. At the head of the estuary is the town of Maldon, which is a centre of salt production. The other major settlement is the town West Mersea, of Mersea Island, on the northern seaward side. Numerous other villages are on its banks.
Within the estuary is Northey Island which was the location for the first experiments in the UK in 'managed retreat', i.e. creating saltmarsh by setting sea walls back from what are perceived to be unsustainable positions. The area is notable as a breeding area for little tern (Sternula albifrons) and as a transit point for ringed plover (Charadrius hiaticula).
Pied avocet (Recurvirostra avosetta)
Black-tailed godwit (Limosa limosa islandica)
Dark-bellied brent goose (Branta bernicla bernicla)
Dunlin (Calidris alpina alpina)
Eurasian golden plover (Pluvialis apricaria)
Grey plover (Pluvialis squatarola)
Hen harrier (Circus cyaneus)
Common redshank (Tringa totanus)
Ringed plover (Charadrius hiaticula)
Ruff (Philomachus pugnax)
Common shelduck (Tadorna tadorna)The Estuary is also the current mooring location for the Ross Revenge, the home of former pirate station Radio CarolineC. cyaneus
C. cyaneus may refer to:
Ceanothus cyaneus, the San Diego buckbrush or lakeside ceanothus, a flowering plant species found in California and Baja California
Circus cyaneus, the hen harrier or Northern harrier, a bird of prey species that breeds throughout the northern parts of the northern hemisphere
Copadichromis cyaneus, a fish species found in Malawi, Mozambique and TanzaniaCladotaenia circi
Cladotaenia circi is a tapeworm of the genus Cladotaenia that has birds of prey as its definitive host, such as the western marsh harrier (Circus aeruginosus), hen harrier (Circus cyaeneus), and peregrine falcon (Falco peregrinus) in Europe. It has been found at low frequencies in small mammals, such as the bank vole (Myodes glareolus) and common vole (Microtus arvalis) in Hungary and the marsh rice rat (Oryzomys palustris) in Florida.Crymlyn Bog
Crymlyn Bog (Welsh: Cors Crymlyn) is a nature reserve and a designated Site of Special Scientific Interest of international significance, near Swansea, south Wales.
It is the largest area of lowland fen in Wales and lies immediately to the eastern side of Kilvey Hill just north of the industrial area of Crymlyn Burrows.
Plantlife found in the bog is more typical of that found in East Anglia. Habitats range from swamps, carr (fen), water meadows and tall reed beds to waterlogged scrub consisting mainly of willow, where wetter areas merge with woodland. There are a number of plants found in the wetland that are rare in Great Britain. Examples of these include the slender cotton grass and lesser water plantain.
In 2003, surveys of Crymlyn Bog, Pant-y-Sais Fen and the inter-connecting wetlands identified the area as one of only three locations in the UK at which the fen raft spider is found. The extent of the population is unknown but the quality of habitat at the site is considered good enough for the population to be stable.The reserve is a haven for birds. Predatory visitors like the hen harrier, buzzard, hobby and the occasional marsh harrier visit the site regularly. The site provides an important refuge for a range of wetland birds like the bittern, water rail, sedge and reed warblers, bearded tit and grey heron, which can often be seen or heard there.
There is a visitor centre in the bog, which is frequented by nature and bird watching enthusiasts.Dengie nature reserve
Dengie nature reserve is a 3,105 hectare biological and geological Site of Special Scientific Interest between the estuaries of the Blackwater and Crouch near Bradwell-on-Sea in Essex. It is also a National Nature Reserve, a Special Protection Area, a Nature Conservation Review site, a Geological Conservation Review site and a Ramsar site. It is part of the Essex estuaries Special Area of Conservation. An area of 12 hectares is the Bradwell Shell Bank nature reserve, which is managed by the Essex Wildlife Trust.It consists of large, remote area of tidal mud-flats and salt marshes at the eastern end of the Dengie peninsula . The Chapel of St Peter-on-the-Wall overlooks some of the site.
It is a wetland of international importance and provides habitats for:
Bar-tailed godwit (Limosa lapponica)
Hen harrier (Circus cyaneus)
Grey plover (Pluvialis squatarola)
knot (Calidris canutus)
Black-tailed godwit (Limosa limosa islandica)
Dunlin (Calidris alpina alpina)
Lapwing (Vanellus vanellus)
Oystercatcher (Haematopus ostralegus)
Dark-bellied brent goose (Branta bernicla bernicla)
Cormorant (Phalacrocorax carbo)
Great crested grebe (Podiceps cristatus)Eilean na Muice Duibhe
Eilean na Muice Duibhe, also known as Duich Moss, is an area of low-level blanket mire on the island of Islay, off the west coast of Scotland. Located south of the town of Bowmore and with an area of 576 hectares, the area has been protected as a Ramsar Site since 1988.The site includes an unusual transition from blanket bog to raised mire habitats. It supports an internationally important population of white-fronted geese, with 2% of the Greenland population overwintering at the site. Breeding birds include the common redshank, red-throated loon and hen harrier.As well as being recognised as a wetland of international importance under the Ramsar Convention, Eilean na Muice Duibhe has also been designated a Special Protection Area.Fertő-Hanság National Park
Fertő-Hanság National Park (Hungarian: Fertő-Hanság Nemzeti Park) is a national Park in North-West Hungary in Győr-Moson-Sopron county. It was created in 1991, and officially opened together with the connecting Austrian Neusiedler See National Park the same year (both parks are attached to Lake Neusiedl/Lake Fertő). The park covers 235.88 km², and consists of two main areas.
Lake Fertő is the third largest lake in Central-Europe, and the westernmost of the great continental salt lakes of Eurasia. Because of the shallow level of water and the prevailing wind, the size and shape of the lake changes very often. The area gives home to various kinds of birds, like the great egret, purple heron, common spoonbill and greylag goose. During the migration season species of the family Scolopacidae appear. Rare birds include red-breasted goose, white-tailed eagle and hen harrier. The lake is inhabited by weatherfish, northern pike and ziege. On the meadows west from the lake vegetation of rare plants like the yellow lady's slipper, fly orchid, the Hungarian iris and Iris pumila and various butterfly species can be found, while the eastern puszta areas are covered by Puccinellia peisonis, Aster tripolium, A. pannonicum and Suaeda maritima.Forest of Bowland
The Forest of Bowland, also known as the Bowland Fells, is an area of barren gritstone fells, deep valleys and peat moorland, mostly in north-east Lancashire, England with a small part in North Yorkshire (before 1974, some of the area was in the West Riding of Yorkshire). It is a western spur of the Pennines and was once described as the "Switzerland of England".The Forest of Bowland has been designated an Area of Outstanding Natural Beauty (AONB) since 1964.
The Forest of Bowland AONB also includes a detached part known as the Forest of Pendle separated from the main part by the Ribble Valley, and anciently a forest with its own separate history. One of the best-known features of the area is Pendle Hill, which lies in Pendle Forest. There are more than 500 listed buildings and 18 scheduled monuments within the AONB.
Bowland survives as the north-western remainder of the ancient wilderness that once stretched over a huge part of England, encompassing the Forest of Bowland, Sherwood Forest (Nottinghamshire), the New Forest (Hampshire) and Savernake Forest (Wiltshire). While the Trough of Bowland (the valley and high pass connecting the Wyre (at Marshaw) and Langden Brook and dividing the upland core of Bowland into two main blocks) represents the area, to many, on account of its popularity, it is in fact only a small part of the wider Forest of Bowland area.
The hills on the western side of the Forest of Bowland attract walkers from Lancaster and the surrounding area. Overlooking Lancaster is Clougha Pike, the western-most hill. The hills form a large horseshoe shape with its open end facing west. Clockwise from Lancaster the hills are Clougha Pike (413 m or 1,355 ft), Grit Fell (468 m or 1,535 ft), Ward's Stone (561 m or 1,841 ft), Wolfhole Crag (527 m or 1,729 ft), White Hill (544 m or 1,785 ft), Whins Brow (476 m or 1,562 ft), Totridge (496 m or 1,627 ft), Parlick (432 m or 1,417 ft), Fair Snape Fell (510 m or 1,670 ft), Bleasdale Moor (429 m or 1,407 ft), and Hawthornthwaite Fell (478 m or 1,568 ft). Considerable areas of the Bowland fells were used for military training during the Second World War, and there are still unexploded bombs in some areas.
The area contains the geographic centre of Great Britain which is close to the Whitendale Hanging Stones, around four miles (6 km) north of Dunsop Bridge. The historical extent of Bowland Forest is divided into two large administrative townships, Great Bowland (Bowland Forest High and Bowland Forest Low) and Little Bowland (Bowland-with-Leagram), but the modern-day AONB covers a much larger area.Geltsdale
Geltsdale is a hamlet in Cumbria, England, to the southeast of Castle Carrock.
The Geltsdale Reservoir railway ran in the vicinity.
The local landscapes are under several levels of protection. Two of the protected areas cover a large area:
the North Pennines Area of Outstanding Natural Beauty
the North Pennines Moors Special Protection Area (147,276 ha)Geltsdale & Glendue Fells Site of Special Scientific Interest has an area of 8,059 ha, and is one of the SSSIs which underlie the SPA.
Geltsdale RSPB reserve is a 5,000 ha nature reserve within the SSSI. It mainly moorland and is managed by the Royal Society for Protection of Birds for upland birds such as black grouse and hen harrier.Geltsdale RSPB reserve
Geltsdale RSPB reserve is a nature reserve in Geltsdale, Cumbria, England. The Royal Society for the Protection of Birds manages the site for upland birds such as the hen harrier and black grouse.Großes Meer
The Großes Meer is a naturally formed fen lake (Niedermoorsee) in north Germany that lies between Aurich and Emden near Bedekaspel in the Südbrookmerland region, on the edge of the East Frisian Geest where it transitions to the Ems marshes. The lake is the fourth largest in the state of Lower Saxony with an area of open water of about 289 hectares (710 acres) (and reed bed covering about 400 hectares (990 acres)). The Großes Meer is – apart from a few deeper spots – only 0.5 to 1.0 metre deep. It is divided into two, almost separate, bodies of water (northern and southern sections). One feature is that the average water level lies 1.4 metres below sea level due to artificial drainage.
The nature reserve of South Großes Meer (Südteil Großes Meer) was established in 1974 and is surrounded by a 2,500 hectares (6,200 acres) large protected landscape. The northern part, by contrast, is used as a leisure and recreation area and has facilities for angling and water sports. It may not be used by motor boats, however.
With its extensive belt of reed-beds and the adjacent wetlands the Großes Meer and its surrounds are a breeding area and habitat of regional importance. Black-tailed godwit, snipe, lapwing, short-eared owl, marsh harrier, hen harrier, bittern, sedge warbler, bluethroat and reed bunting are a few of the species of breeding bird that are important from a conservation perspective. In winter huge flocks of greylag geese and greater white-fronted geese shelter here.
Southwest of the Großes Meer lies the Kleines Meer, also called the Hieve. West of the northern section of the Großes Meer is the Loppersumer Meer. The former Siersmeer and Heerenmeeder Meer in the southern part of the nature reserve have completely silted up and now form a large expanse of sedge with transitions to grey willow bushes.Harrier (bird)
A harrier is any of the several species of diurnal hawks sometimes placed in the Circinae sub-family of the Accipitridae family of birds of prey. Harriers characteristically hunt by flying low over open ground, feeding on small mammals, reptiles, or birds. The young of the species are sometimes referred to as ring-tail harriers. They are distinctive with long wings, a long narrow tail, the slow and low flight over grasslands and skull peculiarities. The harriers are thought to have diversified with the expansion of grasslands and the emergence of C4 grasses about 6 to 8 million years ago during the Late Miocene and Pliocene.Montagu's harrier
The Montagu's harrier (Circus pygargus) is a migratory bird of prey of the harrier family. Its common name commemorates the British naturalist George Montagu.Northern harrier
The northern harrier or marsh hawk (Circus hudsonius or Circus cyaneus hudsonius) is a bird of prey.
It breeds throughout the northern parts of the northern hemisphere in Canada and the northernmost USA. While many taxonomic authorities split the northern harrier and the hen harrier into distinct species, others consider them conspecific.It migrates to more southerly areas in winter with breeding birds in more northerly areas moving to the southernmost USA, Mexico, and Central America. In milder regions in the southern US, they may be present all year, but the higher ground is largely deserted in winter.Pallid harrier
The pale or pallid harrier (Circus macrourus) is a migratory bird of prey of the harrier family. The scientific name is derived from the Ancient Greek. Circus is from kirkos, referring to a bird of prey named for its circling flight (kirkos, "circle"), probably the hen harrier and macrourus is "long-tailed", from makros, "long" and -ouros "-tailed".It breeds in southern parts of eastern Europe and central Asia (such as Iran) and winters mainly in India and southeast Asia. It is a very rare vagrant to Great Britain and western Europe, although remarkably a juvenile wintered in Norfolk in the winter of 2002/2003. In 2017 a pair of pallid harriers nested in a barley field in the Netherlands; they raised four chicks.This medium-sized raptor breeds on open plains, bogs and heathland. In winter it is a bird of open country.Ruabon Moors
Ruabon Moors are an area of upland moorland in Wales to the west of Ruabon and Wrexham. They lie partly within Wrexham county borough and partly within Denbighshire.
In the northern part of the moors are the areas known as Minera Mountain and Esclusham Mountain. Further south are Ruabon Mountain and Eglwyseg Mountain. In the west the moors reach their greatest height at Cyrn-y-Brain, 565 metres (1,854 ft) above sea level. To the north and north-east, the moors are bounded by Minera Limeworks and the Clywedog valley. In the east they slope down to the villages of Rhosllannerchrugog and Ruabon. There are several small reservoirs in this area. At the southern edge of the moors the cliffs of Eglwyseg Rocks overlook the River Dee and the Vale of Llangollen. On the western side there are more cliffs at World's End while the Horseshoe Pass separates the moors from Llantysilio Mountain. Llandegla Forest, a large conifer plantation, covers the north-western side.
Ruabon Moors are part of a Site of Special Scientific Interest and hold a wide variety of plant and animal life. Large parts of the moors are covered with heather. Where there are outcrops of limestone on the surface a number of scarce plants can be found such as prickly sedge, dark red helleborine and rigid buckler-fern.
The moors are managed for red grouse shooting. Huge numbers were shot in the past (an average of 4658 per year from 1900 to 1913) but numbers have now decreased dramatically. The area is also home to black grouse and a major conservation programme has caused their population to increase in recent years. Other birds which can be seen include peregrine falcon, merlin, hen harrier, short-eared owl and ring ouzel.
The area has been modified by human activity since prehistoric times when people built cairns and cleared the original forest. Mining has taken place in the area since Roman times and there are still many shafts of disused lead, zinc, silver and coal mines dotting the area. During the Second World War bombs were dropped on the moors by German planes heading to and from Liverpool and a number of bomb craters can still be seen today.
The area is popular with walkers and rock-climbers and the Offa's Dyke Path crosses the region.
It is rife with controversy after two satellite tagged hen harriers mysteriously disappeared here in 2018 and a raven was found poisoned in 2019.Simon Barnes
Simon Barnes is an English journalist. He was Chief Sports Writer of The Times until 2014, and also wrote a wildlife opinion column in the Saturday edition of the same newspaper. He has also written three novels.Barnes was educated at Emanuel School, and studied English Literature at the University of Bristol, which awarded Barnes an honorary Doctorate in 2007.After beginning his journalism career on local newspapers in Britain, he travelled to Hong Kong, where he wrote for travel magazines and, briefly, the South China Morning Post. After his return to Britain, he became a sports writer for The Times, being promoted in time to the position of Chief Sports Writer. He is the author of 16 books including three novels. His latest book, Birdwatching With your Eyes Closed: An Introduction to Birdsong, was published in 2011. Barnes has also appeared in a number of programmes on BBC Radio 2, including a reading of his book, How to Be a Bad Birdwatcher.
Barnes lives in Norfolk. He was on The Times team at the 2012 London Olympics, the seventh summer Games that he has covered for the newspaper. In March 2009 he was runner-up in the Sports Journalists' Association's 'Sports Columnist of the Year' award, an award he won in 2008.
In June 2014 Barnes was sacked by The Times after 32 years employment, the newspaper having informed him it could no longer afford to pay his salary. Speculation in some sections of the UK media that the real reason may have been Barnes's outspoken views expressed in his wildlife opinion column. The column blamed illegal activity by red grouse shooting interests on the continued persecution and near extinction of the hen harrier in England. Writing in his new website and blog which he began after leaving The Times in 2014, Simon Barnes wrote: "Certainly I have annoyed some powerful people."WWT Martin Mere
WWT Martin Mere is a wetland nature reserve managed by the Wildfowl and Wetlands Trust at Tarlscough, Burscough, Lancashire, England, on the West Lancashire Coastal Plain, 6 miles (10 km) from Ormskirk and 10 miles (16 km) from Southport (Merseyside). It is one of ten reserves managed by the charity, and it is designated an SSSI (Site of Special Scientific Interest), an SPA (Special Protection Area) and a Ramsar Site.
The name of the centre comes from the mere on the west side of the reserve which is ringed by 11 observation hides. On the east side of the reserve there are a number of pens providing habitats for birds from Africa, Australasia, North America, South America, Siberia, and Asia.
Martin Mere has its own "Domesday Book", listing (for 2002) 517 species of plant, 287 species of fungus and 1,368 species of invertebrate. 284 species of bird have passed through the reserve, as well as 28 species of mammal and 19 species of fish.
This reserve is at its best in winter, attracting huge flocks of pink-footed geese and wigeon, many whooper swans and occasional rarer birds such as the snow goose.
It is also excellent for wintering birds of prey such as hen harrier, peregrine and merlin.
The BBC television programme Autumnwatch was broadcast live from Martin Mere in 2006 and 2007.Western marsh harrier
The western marsh harrier (Circus aeruginosus) is a large harrier, a bird of prey from temperate and subtropical western Eurasia and adjacent Africa. It is also known as the Eurasian marsh harrier. The genus name Circus is derived from the Ancient Greek kirkos, referring to a bird of prey named for its circling flight (kirkos, "circle"), probably the hen harrier. The specific aeruginosus is Latin for "rusty".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), the Papuan harrier (C. 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, the 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.