That such declines are taking place in formerly common birds ... is an event unique in recorded history

Dr Paul Donald, RSPB

They blame modern farming methods, which they say are doing more harm to birds than any other threat. The declines are most marked in the United Kingdom, with much of the rest of western Europe close behind.

There are fears the eastwards expansion of the European Union over the next few years will intensify the threat.

Research by the Royal Society for the Protection of Birds (RSPB), published in the Proceedings of the Royal Society of London, says the intensification of agriculture since 1970 is the culprit.

The authors say it has done more damage to the UK's and Europe's birds than any other single factor, including the effects of climate change, pollution and deforestation.

UK's decline steepest

Across 30 countries, the report says, those with the most intensive farming have suffered the most rapidly declining bird populations.

It says there is a direct link between declines in numbers of once common birds and indicators of farming intensification, including cereal and milk yields and the number of tractors per farm worker.

The cirl bunting enjoys mixed fortunes (Photo: RSPB/Chris Gomersall)

One of the authors, Paul Donald of the RSPB, said: "Our research shows that the UK suffered the worst declines in Europe, but every country recorded a decline in the populations of birds which rely on farmland.

"Declines were most severe in western Europe, with six out of the worst 10 countries being in the EU, where the Common Agricultural Policy (CAP) has fuelled agricultural intensification."

Dr Donald said the situation was without parallel, with some species plummeting at a rate not seen for centuries.

Extraordinary event

"The annual average rate of decline of some of our farmland birds has been greater than that of several species, including the great auk of the north Atlantic and the moas of New Zealand, between their discovery and their global extinction," he said.

"That such declines are taking place in formerly common birds, which have had a long association with man, is an event unique in recorded history."

Dr Donald told BBC News Online: "These declines are extremely rare in nature. What we're seeing here is quite an extraordinary event.

"These birds have been living close to us for thousands of years - they're the hard-to-kill species which have survived for so long.

"The declines may be unique not just so far as the records go, but in the whole of human history."

The RSPB is worried the probable acceptance of 10 eastern European countries into the EU could threaten their farmland birds, including species like the corncrake, great bustard and red-backed shrike.

Change in prospect

It says the conversion of steppe to agricultural land in countries like Ukraine has already driven some birds very close to the brink.

Lapwings, once common, are disappearing (Photo: RSPB/Andrew Hay)

They include the sociable plover, the demoiselle crane and the steppe eagle. But Dr Donald says he is hopeful things will improve.

He said: "The CAP will have to change before the eastern Europeans join, or it will bankrupt the EU.

"Support for farming will increasingly have to be separated from production, so that farmers are paid for enabling skylarks to survive, or landscapes, or whatever.

"Our main concern is that the CAP is modified before these eastern European countries join the EU."