Marsh harriers (Circus aeruginosus) are recognised as harriers by their long, narrow tails, long legs and wings held in a 'V' in flight. This species is the largest of the harriers and has broad, rounded wings. Members of the genus Circus possess an owl-like 'ruff' of facial feathers that disguises very large ear openings, which enable the bird to detect prey species by the noises they produce. The plumage colour is variable, but mainly brown. Females and immature individuals have creamy coloured crowns and throats; mature males have pale-grey wings with a dark brown body and wings. Calls include a lapwing-like mewing and a 'chattering' alarm call (2).
During the breeding season, pairs form which may last for a number of seasons. The spectacular courtship display involves the male flying in circles at a great height over the breeding area before falling close to the ground, performing elaborate sequences of tumbles. Occasionally the female may join him, and the pair lock talons and tumble through the air together. As the season progresses the male may be seen dropping food into the female's talons in mid-air (4). The nest, which may measure up to 80 centimetres in diameter, is constructed on the ground with grass, reeds and sticks by the female. Three to eight eggs are laid from late April, and both parents contribute to feeding the chicks (2).
Hunting occurs at a height of two to six metres above ground; when prey is located the bird suddenly drops down with its talons outstretched. Food taken includes small mammals and birds, carrion and sometimes insects, frogs and fish (2).
A scarce summer visitor to Britain, marsh harriers are also found in Europe, the Middle East, Central and northern Asia, and parts of Africa. In Britain the species mainly breeds in East Anglia, but can be seen on the south and east coast as far north as Scotland whilst it is migrating. It can also occasionally be seen in Wales and Ireland. Small numbers of individuals over-winter in East Anglia, Kent and south Wales (3). There are records of marsh harriers in Britain that date from the Iron Age, about 3000 years ago (2).
Marsh harriers are usually associated with wetlands, as the common name would suggest (2). Breeding occurs amongst reeds or sedges, usually in large reed beds. However there are records of some individuals breeding in cereal fields, or within small areas of reeds located amongst arable land or saltmarsh. Hunting generally occurs over agricultural land or open habitat containing aquatic vegetation (3).
The marsh harrier is classified as Least Concern (LC) on the IUCN Red List (1). Listed under Annex 1 of EC Birds Directive; Appendix II of the Bern Convention and the Birds of Conservation Concern Red List. Protected in the UK under Schedule 1 of the Wildlife and Countryside Act 1981 (3).
The species underwent a decline in numbers in the 18th and 19th centuries due to the effects of habitat drainage and persecution for predating upon game species. The population declined to just a single pair between 1959 and 1971, mainly as a result of egg-shell thinning caused by organochloride pesticides such as DDT. After 1972 the population began to recover; in 1994 there were 129 pairs, and numbers have continued to increase. Current threats include the deliberate disturbance of nesting sites, egg collecting, illegal poisoning and predation by foxes. The small size of reedbed habitats may result in an increased impact of disturbance (3).
The marsh harrier will benefit from the protection and creation of reedbed habitat (2). Egg collecting, nest disturbance and illegal poisoning must be controlled. Prevention of scrub encroachment and the maintenance of suitable water levels will maintain appropriate habitat and deter foxes, the main predator. As this harrier nests in close association with intensive agricultural land, levels of pesticides must be monitored. Research is being conducted on the breeding biology, food and hunting behaviour of the species in Britain and the Netherlands (3).
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