The numbers of corncrake, one of Britain's rarest farmland birds, has fallen suddenly after fewer farmers took up grants to preserve the old-fashioned hay meadows they need to survive.
The endangered but charismatic bird, once one of the country's most popular and iconic farmland birds, had disappeared throughout mainland Britain by 1972 as intensive farming methods led to the loss — and more frequent mowing — of the hay meadows and borders in which they nest.
The decline was so severe that conservationists counted fewer than 450 "calling males" — mature, breeding adults — in its core area on islands off western and northern Scotland in 1993. Ecologists predicted it could have become extinct in the UK by the early 21st century.
Their numbers tripled over the last 15 years to 1,236 in 2007 after ministers introduced grants to reward farmers and crofters who delayed cutting hay until after the breeding season.
Apart from a sudden but unexplained dip in corncrake numbers in 1998, their populations have continued to rise every year. But this year the number of "calling males" fell by nearly 8% to 1,140, raising anxieties about recent reforms of the grants system.
Mark O'Brien, a habitats adviser to the Royal Society for the Protection of Birds Scotland, said this unexpected decline coincided with the introduction of a different, competitive scheme, and a fall in the number of farmers seeking subsidies.
The original scheme rewarded any farmer who signed up by paying them a fixed sum per hectare for delaying mowing, and by agreeing to cut grass from the centre of a field outwards, to allow nesting corncrakes time to escape.
The new rural priority scheme is potentially more generous, by increasing payments further if grass-cutting is delayed from August 1 until September 1, from £271 to £691. However, it is also competitive, forcing farmers to bid for funding without being guaranteed a grant, and farmers must also set aside extra grassland nearby.
O'Brien said the RSPB was closely monitoring the impact of this change. "The new scheme is competitive, which does put quite a few folk off," he said. "We would get very concerned if this decline continued for a couple of years."
Crofters and farmers can also apply for a special corncrake management grant from Scottish Natural Heritage, while the RSPB, SNH and Scottish Crofting Foundation runs a smaller scheme for land-holders who cannot apply for the mainstream grants.
The corncrake is a migratory bird which returns to nest in the UK from Africa every spring. It survives in small numbers on Hebridean and Argyll islands off the west coast of Scotland, particularly Coll, Islay, Tiree, Iona, and Colonsay, as well as Orkney in the north.
It is known for its distinctive "crex, crex" call, likened by birders to the rasping sound of a comb being dragged over the edge of a credit card.
Apart from Sweden and Finland, the species has also declined across mainland Europe, where more than half its population has been lost in more than 10 countries and nearly every country has seen losses of at least a fifth.