The trust published research showing the goldfinch, linnet, reed bunting and skylark had all declined rapidly on cropfields over the past 15 years.
Seed-eating birds have done badly on all kinds of farmland - numbers overall fell by 40 per cent between 1977 and 1991. The trust is convinced that modern farming bears much of the blame. This is certainly the case for the four species whose numbers have declined particularly fast on cropfields, the trust says.
Its research was based on observation and recording of the birds, year after year, by trust volunteers on 200 plots of farmland, nearly all in lowland England and Wales.
Two of the trust's staff, John Marchant and Richard Gregory, analysed the results and obtained reliable nation-wide trends for nine seed-eaters.
Only two - the chaffinch and greenfinch - increased their populations slightly. The other seven showed declines over the 15 years ranging from 19 per cent for the yellowhammer to 81 per cent for the tree sparrow.
The goldfinch, linnet, reed bunting and skylark fared worst on the arable plots - the most common type of farmland in the lowlands. The trust estimates that the skylark population has fallen by three million since the mid 1970s.
The trust's director, Jeremy Greenwood, said cropfields were becoming useless habitats for birds as farmers became more efficient at boosting yields and eliminating weeds. 'These results are devastating since these species used to be the sort of common birds one would expect to find on ordinary arable land.
'Autumn sowing deprives birds of stubbles as food resources during the winter. For many species our arable crops do not now provide any significant resources for them to exploit at any time of year.
'Farming is a business and farmers shouldn't be blamed for doing their job so well that wild birds are being displaced. But our wildlife is a national resource and the nation should be aware this is happening.'
The picture is not entirely gloomy. The census results take in dozens of other species found on farmland, from crows to swallows, and numbers rose very slightly overall.
The trust hopes the EC's set-aside regime, which removes 18 per cent of Britain's arable land from crop production, offers the seed-eaters hope for a recovery. Under the right management, this land provides good ground for feeding and breeding.
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