Britain's bird population has plummeted by 44 million in four decades, according to a study carried out with the help of volunteer ornithologists.
The dramatic decline in numbers – equivalent to one bird for every person in England and Wales – has been caused by changes in farming methods and the weather, conservation groups say.
Figures collated by organisations including the Royal Society for the Protection of Birds and the British Trust for Ornithology found that the number of nesting birds had slumped from 210 million in 1966 to 166 million today.
In their report, The State of the UK's Birds, they warn that while numbers for some species, such as the house sparrow, show signs of recovery, further declines are inevitable as birds cope with changes to the environment and conservationists battle for investment in wildlife-friendly farming to be maintained.
There is particular concern that spending on wildlife protection in Britain will be disproportionately slashed as a result of cuts in the EU budget this week, with the monitoring of the health of the bird population dependent on continued support from volunteer birdwatchers. Up to 20 per cent could be cut from the EU's rural development budget.
The differing fates of two dove species encapsulate the shifting fortunes of the UK's birds. There are estimated to be only 14,000 breeding pairs of turtle doves, a significant drop from their 140,000 peak in 1966. But there are now one million collared doves, despite coming to Britain only in 1955.
Another bird bucking the trend is the blackcap, whose numbers have jumped by 222 per cent to 1.2 million. Unlike other warblers that migrate to Africa, the blackcap is staying closer to home in Europe.
"Our bird population has been on a roller-coaster ride and it will continue," said Grahame Madge of the RSPB.
Dr Tim Hill, Natural England's chief scientist, said the report was "a great example of 'citizen science' in action" with most of the data coming from observations by volunteer ornithologists.