for bitterns within the reed beds. The grazing regime was instituted following investigations into similar schemes in Sweden and Denmark. The heathland and acidic grassland areas of Minsmere are managed by grazing, heather and scrub control and removal of trees and unwanted western gorse. The areas of gorse and scrub remaining are cut in rotation to keep the gorse short and dense, providing a scrub structure optimal for nightingales. In 1989, of arable land were purchased in a project to recreate lowland heath and acidic grassland habitat by acidification of the soil, the aim being to join fragmented patches of heathland together and to provide increased habitat for the stone-curlew, woodlark and nightjar, three threatened bird species. Methods used to acidify the land, which had been arable farmland for 150 years, included grazing by sheep or the addition of sulphur, either with bracken and heather waste, or on its own, followed by reseeding. Fauna and flora Minsmere's large size and variety of different habitats, some of which are scarce elsewhere in the UK, make it attractive to many species of animals and plants; around 5800 species have been recorded on the reserve. Birds As of 2017, 342 bird species have been sighted at Minsmere, of which 230 are annual and more than 100 have bred. In the 1990s the bittern was in serious decline with only one booming male on the reserve. Creation of ditches and pools and better water-level management led to 9–12 males being present annually, and application of these techniques elsewhere has revived the fortunes of this species in the UK as a whole. The stone curlew has also benefited from the creation of suitable bare-ground nesting habitat, and the reserve's population is now nearly 10 pairs each year, against a single pair in Suffolk in the mid-1990s. The avocet first started its recolonisation of Britain in 1947, four pairs breeding a month after the reserve was acquired by the RSPB. Numbers at Minsmere now vary between 40 and about 140 pairs per year. In 1971, the only nesting pair of marsh harriers in the UK were at Minsmere. The population of this polygynous species reached 17 nesting females in 2007, up from the more typical 8 to 10. Other important species are bearded tits, woodlarks, nightjars in open habitats, nightingales in the woodlands, and Dartford warblers, which returned to Minsmere's heaths in the mid-1990s, having been