By Environment Correspondent Alex Kirby

Birdlovers believe the drastic loss in skylark numbers in the UK in the last three decades is largely the result of farmers sowing cereals in the autumn, not the spring.

A study of 995 skylark nests, between 1996 and 1999, on 24 farms in East Anglia, Oxfordshire and Dorset, found twice the density of skylarks in fields sown with spring cereals compared with crops grown in the autumn.

Before a spring crop is sown, the stubble from the previous crop is left unploughed, and this provides food and cover for the birds during the winter.

The Royal Society for the Protection of Birds (RSPB), which carried out the research, says spring-grown crops also provide safer nesting sites and encourage the birds to make more attempts at raising a brood.

"Skylarks like short vegetation, and spring crops remain relatively short throughout the breeding season", the RSPB's Alasdair Bright told BBC News Online.

Easy prey

"Winter crops grow high, and leave no bare soil in the field. So the birds nest on the only clear earth they can find, the parallel lines through the crop left by the tractor wheels.

"They stand out there like sore thumbs, and they're a sitting target for predators.

"With spring crops they feel safer, so they breed more often and probably raise more young each time they do."

The RSPB says spring cereals are also more skylark-friendly because they normally have fewer applications of pesticides than winter crops.

Between 1968 and 1996 the area of spring-grown cereals in the UK fell from 73% to 16% of the country's total cereal area, a result of the European Union's Common Agricultural Policy and its emphasis on production.

From 1972 to 1996 the total UK skylark population fell by 60%, and by 75% on farmland.

The British Trust for Ornithology says cereals are one of the most important skylark habitats, accounting for 40% of farmland skylarks in England and Wales, and 34% in Scotland.

Mark Avery, the RSPB's conservation director, said: "Increasing the area of spring-grown cereals is a feasible solution".

He added: "This is an opportunity not to be missed, and it would go a long way to helping farmers meet the challenge of skylark conservation."

A spokeswoman for the National Farmers Union told BBC News Online: "Part of the pressure for the switch to winter-grown crops has come from retailers, and farmers have been forced to do it to remain cost effective."