Linnet is saved from disaster by oilseed rape

The linnet, the favourite songbird of the Victorians, has been saved from the catastrophic declines now affecting numerous farmland birds, by the country's most unpopular crop, oilseed rape.

The linnet, the favourite songbird of the Victorians, has been saved from the catastrophic declines now affecting numerous farmland birds, by the country's most unpopular crop, oilseed rape.

The garish yellow fields many people feel are quite out of place in the British countryside have provided a lifeline for the small seed-eating bird, while other species such as the corn bunting, the grey partridge and the turtle dove have seen their populations reduced by more than three-quarters in 30 years by the introduction of intensive farming.

The linnet too has been badly affected by the spraying of chemicals across the land in which it feeds - it is down in numbers by more than a third - but it has started to recover by substituting nutrient-packed rape seed for the wild flower seeds on which it previously fed, and which weedkillers have now removed en masse from fields and pastures.

The story of the bird's comeback and the unexpected reason for it has been uncovered by a young scientist working for the Royal Society for the Protection of Birds (RSPB), Darren Moorcroft. He was aided by the fact that the linnet has a physical peculiarity: its chicks have a piece of transparent skin over the gullet, which enables observers to see exactly what a nestling has just eaten.

The linnet is a finch, closely related to the goldfinch and the greenfinch - the male has a red forehead and red breast, while the female is a browny-grey. It is almost a forgotten bird in Britain, but a hundred years ago and earlier it was one of the most popular, frequently kept as a cage bird and prized for its melodious song, which reminds some people of a canary's.

"From about the 1840s until the early years of this century it was probably the most popular cage bird, until it was replaced by the budgerigar," said Roger Caton of the British Bird Council, which represents bird-keepers and breeders. "People used to hold linnet-singing contests in back rooms of pubs."

It features in the well-known music-hall ditty about the troubles of moving house, which begins: "My old man said follow the van, and don't dilly-dally on the way", and continues, "Off went the cart with our home packed in it - I walked behind with me old cock linnet ... "

They were strictly scientific reasons, however, that made Mr Moorcroft, an RSPB conservation officer in the Midlands, choose the linnet as the topic for his PhD thesis at Oxford University: he wanted to investigate the bird's part in the decline of British farmland birds. For three years, at nine sites in Warwickshire, Wiltshire and Oxfordshire, he found and examined no fewer than 912 linnet nests, discovering the diet of the chicks was radically different from that revealed in a survey in the 1960s, before intensive farming took hold.

Then, the nestlings were fed on the seeds of wild plants, such as charlock, groundsel, shepherd's purse and buttercups. Now they eat dandelion seeds early in the breeding season, and, unripe and therefore more palatable seeds of rape as soon as they become available. No less than 75 to 80 per cent of the diet of all linnet chicks is rape seeds, Mr Moorcroft found.

Oilseed rape, once virtually unknown in the UK, has in less than 30 years become Britain's third most widely grown arable crop, after wheat and barley. It was introduced after Britain entered the European Community in 1973 because farmers could take advantage of generous subsidies from Brussels. It now covers about half a million hectares. Yet many people feel its arrival was a mixed blessing as its bright yellow fields seem alien to the subtle colours of the British countryside.

In the late eighties, new rape varieties that did not contain erucic acid and glucosinolates were planted - so the oil could be used in human food. This change, Mr Moorcroft says, saved the linnet, which until then was swiftly declining.

The year the new varieties were first planted, 1987, was the year the linnet's population stopped dropping and started to rise. "The upturn in its fortunes seems to correlate very nicely with the expansion of oilseed rape and changes in the varieties grown," he said.

In another experiment, he looked at linnets in an area of Norfolk where there was little rape grown, and their breeding success was much reduced.