Western Marsh-harrier, Circus aeruginosus

The Western Marsh-harrier (Circus aeruginosus) is a sizable harrier, a bird of prey from subtropical and temperate western Eurasia and adjacent Africa. It’s also known as the Eurasian Marsh-harrier.

Formerly, a number of relatives were included in C. aeruginosus, which was known then as “Marsh Harrier”. The related taxa are now usually 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) found in Australasia and the Madagascar Marsh-harrier (C. maillardi) found in the western Indian Ocean islands.

The Western Marsh-harrier is frequently divided into two subspecies, the widely migratory C. a. aeruginosus, which is found across most of its range, and C. a harterti, which is an all year resident in north-west Africa.

It is 43 to 54 cm in length, and has a wingspan of 115 to 130 cm and a weight of 400 to 650 g in males and 500 to 800 g in the females. It’s a large and bulky harrier with fairly broad wings, and has a strong and strange sexual dichromatism. The male’s plumage is mostly a cryptic reddish-brown with lighter yellowish colored streaks, which are particularly prominent on the breast. The shoulders and head are mostly pale grayish-yellowish colored. The rectrices and the secondary and tertiary remiges are pure grey, the latter contrasting with the brown forewing and the black primary remiges at the tips of the wings. The underside and upperside of the wing look similar, though the brown is lighter on the underwing. Whether from below or the side, flying males appear characteristically three-colored brown-grey-black. The feet, legs, irides and the cere of the black bill are yellow.

The female bird is almost completely chocolate brown. The throat, top of the head, and the shoulders have a conspicuously lighter yellowish color; this can be clearly enclosed and very contrasting, or be more washed-out, resembling the colors of the males head. But the eye area of the female is always darker, making the light colored eye stick out, while the males head is altogether not very contrastingly colored and the female lacks the grey tail and patch on the wing. The juveniles look much like the females, but generally have less yellow, especially on the shoulders.

There is a rare hypermelanic morph with largely dark colored plumage. It’s most often found in the east of the species’ range. The juveniles of this morph may look entirely black while in flight.

The 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 sub arctic Scandinavia. It’s rare, but increasing in Great Britain where it has spread as far as eastern Scotland. In the Middle East, there are populations in Turkey, Iran and Iraq, while in Central Asia the range stretches eastwards as far as north-west China, Mongolia and the Lake Baikal region of Siberia.

The majority of the populations of the Western Marsh-harrier are migratory or dispersive. Some of the birds winter in milder regions of southern and western Europe, while the 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, Tunisia, and Algeria.

Vagrants have reached Iceland, the Azores, Sumatra, and Malaysia. The first documented record for the Americas was one bird reportedly photographed on December 4, 1994 at Chincoteague National Wildlife Refuge in Accomack County, Virginia. Afterwards, there were confirmed records from Guadeloupe and from Laguna Cartagena National Wildlife Refuge on Puerto Rico.

Like other marsh-harriers, it’s strongly associated with wetland areas, especially those that are rich in Common Reed. It can also be met with in variety of other open habitats, such as grassland and farmland, particularly where these border marshland. It’s a territorial bird during the breeding season, and even in the winter it seems less social than other harriers, which frequently father in large flocks. But this is most likely because of their 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 outbreaks of locusts. Still, on Keoladeo National Park in India, around 100 Eurasian Marsh Harriers are observed to roost together each November/December; they come together in tall grassland dominated by Desmostachya bipinnata and Vetiver, but where this is too disturbed by human activity, they will use floating carpets of Common Water Hyacinth instead – the choice of such roosting sites may be to give early warning of predators, which will conspicuously rustle though the plants if they attempt to sneak up on the resting birds.

It hunts in a typical harrier manner, gliding low over flat open ground, searching for prey with its wings held in a shallow V-shape and often with its legs dangling.

It mostly feeds on small mammals, insects, small birds, reptiles and frogs.

The initiation of the breeding season varies from mid-March to early May. Western Marsh-harrier males frequently pair with two and occasionally three females. Pair bonds usually last for a single breeding season, but some pairs stay together for several years.

The ground nest consists of sticks, grasses, and reeds. It’s usually constructed in a reedbed, but the species will nest in arable fields as well. There are between three and eight eggs in a usual clutch. The eggs are oval shaped and white colored, with a bluish or greenish tinge when recently laid. The eggs are incubated for 31 to 38 days and the young birds fledge after 35 to 40 days.

The Western Marsh-harrier numbers decreased in many areas between the 19th and the late 20th centuries because of persecution, excessive pesticide use and destruction of their habitat. It’s 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 area. 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 avoided and today it is classified as Species of Least Concern by the ICUN.

Image Caption: Eurasian Marsh Harrier Circus aeruginosus at/ near Hodal in Faridabad District of Haryana, India. Credit: J.M.Garg/Wikipedia (CC BY-SA 3.0)