Marsh harrier  (Circus aeruginosus)

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).