Species Guide: Western Marsh Harrier (Circus aeruginosus)
Family: Accipitridae
The Western Marsh Harrier is a large, long-winged raptor inhabiting reedbeds, marshes, and wet meadows across Europe, parts of Asia, and northwest Africa. It is a widespread species, often migratory, and among the most distinctive birds of extensive wetlands; a skilled low-flying hunter of small vertebrates and large invertebrates.
Appearance
Male
Adult males are strikingly patterned, with a pale, creamy-yellow head and shoulders contrasting against a predominantly reddish-brown body and paler, streaked underparts. Grey on the flight feathers (secondaries and tertials) creates a two-toned effect in flight; the wingtips are sharply darker. Males are smaller and slimmer than females.
Female
Females are larger and generally browner and more streaked than males, with a cream or buff crown and throat but an overall darker, richer brown plumage. They are bulkier in appearance and often show more mottling across the body and wings.
Juvenile
Juveniles resemble darker versions of females: warm brown plumage with heavy streaking and a paler head. As they age, they gradually acquire adult sexual plumage differences; males develop the paler head and grey panels on the wings in their first year or two.
Diet
Western Marsh Harriers are opportunistic and generalist predators. Their diet typically includes small mammals (voles, rats), small to medium-sized birds (waders, ducks, passerines), frogs and other amphibians, large insects, and occasionally fish and carrion. They hunt by quartering low over reedbeds, marshes, or fields and dropping onto prey; they will also take food from shallow water or capture birds in flight. Diet composition varies seasonally and regionally depending on prey availability.
Habitat
Preferred breeding habitat is extensive reedbeds, tall marsh vegetation, and wetland mosaics (reedbeds with adjacent pools, wet grassland, and sedge). They also use inland wetlands, river margins, and, in some areas, wet agricultural land. Many populations are migratory: northern and eastern breeders move south in winter to milder parts of southern Europe, Africa, Arabia, or south Asia, while some populations (for example, in NW Africa) may be resident year-round.
Summer
Resident
Winter
Vagrant
Behavior
Marsh Harriers fly with long wings held in a shallow V, quartering slowly over habitat as they search for prey. They can be solitary or occur in loose pairs; males may mate with more than one female in a season (polygyny is recorded, though it is not the rule everywhere). Courtship displays include spectacular aerial acrobatics and talon-locking chases.
Call
The species’ vocalisations are relatively harsh and low: a rolling “krrr” or churr-type call, and croaks are common, used most often near the nest or during alarm and territorial interactions. They are not especially vocal compared with some passerines, but calls are readily heard around nests and during chases.
Life cycle and breeding
Fledging: chicks hatch asynchronously and fledge after roughly 35–45 days, remaining dependent on parents for some weeks after first flight. Most pairs raise one brood per season.
Nest: built in large reedbeds or tall marsh vegetation, often on a platform of reeds and sticks above water or damp ground.
Clutch size: typically around 3–5 eggs (records vary; 3–7 or occasionally more are reported).
Incubation: about 30–38 days; primarily the female incubates while the male supplies food.
Biometrics2
| Length | 48-56 cm |
| Wing Span | 115-130 cm |
| Body Weight | 500-800 grams |
| Longevity | 6 Years |
Natural Predators
Adult marsh harriers have few natural predators because of their size, but eggs and chicks are vulnerable to mammals (foxes, raccoon dogs where present), large gulls and corvids (which may take eggs or nestlings), and occasionally other raptors. Nest predation and disturbance are important local pressures; marsh harrier adults may be killed by larger raptors on rare occasions, and collisions or poisoning (lead, pesticides) also represent non-predatory mortality.
Relationship to Humans
People have long noticed harriers: their low, deliberate hunting flight and reedbed lifestyle give them a place in wetland folklore and symbolism. Harriers are sometimes associated with cleverness and guardianship in popular symbolism; broader compilations of bird fable and legend include harriers among birds with mythic or moral roles (see classic compilations of bird lore). Historically, like many raptors, marsh harriers suffered from direct persecution (shooting, egg collection), habitat drainage, and pesticide use; in some areas, they were once locally extirpated. More recently, they are a conservation success story in parts of Europe where legal protection, reedbed restoration, and reduced pesticide use have allowed recovery. At the same time, conflicts with agriculture (perceived predation on gamebirds or ground-nesting waders) and illegal persecution continue in some regions.
Conservation Status
Global status: Least Concern (IUCN Red List); the species remains widespread and relatively numerous across its large range. Trends vary regionally.
Regional trends: In many parts of Europe, the Western Marsh Harrier suffered dramatic declines during the 19th and 20th centuries (habitat loss, persecution, pesticides) but has made marked recoveries in recent decades thanks to legal protection and habitat restoration. In the UK and parts of western Europe, its numbers have increased from low levels, and breeding is now well established at many reedbeds; the species is still monitored because local declines or threats (wetland loss, persecution, shooting during migration in some Mediterranean areas) persist. In some countries or local populations (e.g., restricted resident populations), vulnerabilities or declines remain and require conservation attention.
U.K.
Conservation Status
Global
Conservation Status
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References
- Lovette, I. et al. (2016) The Cornell Lab of Ornithology, handbook of bird biology. Third edition. Chichester: Wiley. [Accessed 31/10/2025]
CITATIONS
- By IUCN Red List of Threatened Species, species assessors and the authors of the spatial data., CC BY-SA 3.0, [Accessed 31/10/2025] ↩︎
- RSPB [Accessed 31/10/2025] ↩︎
