Intensive farming practices have caused a sharp decline in kestrel numbers in recent years, according to the RSPB.
The latest Breeding Birds Survey (BBS) shows that the number of kestrels plunged by 36% between 2008 and 2009.
The mysterious disappearance of thousands of birds in one year follows a long-term decline in which the kestrel population has dropped by a fifth since the mid-1990s, according to the survey by the British Trust for Ornithology (BTO).
The Royal Society for the Protection of Birds (RSPB) blamed the drop in numbers on a combination of harsh winters and damaging changes in farming practices.
Grahame Madge, of the RSPB, said: “We think that changes in the countryside are partly responsible for the decline in kestrel numbers.
“Birds like the kestrel are dependent on wildlife-friendly farming practices. Where you have areas of grassland, such as field margins and beetle banks, kestrels will thrive and find food.
“In intensively farmed areas birds will not do as well.
“We believe that the 20% decline is partly due to changes in the countryside and harsh winters.
“Therefore, it is vital that wildlife friendly farming practices continue if we are going to stop the decline of the kestrel, one of the most charismatic birds in our countryside.”
However, the Country Land and Business Association (CLA) said it was disappointed that the RSPB had partly blamed the sharp fall in kestrel number on intensive farming.
CLA President William Worsley said: “The BTO report states that the kestrel population has only declined recently. It was stable between the start of the survey in 1994 until around 2005.
“It is clearly not the case that farming has become more intensive in the past five years. In fact, with the introduction of the Single Payment Scheme, the opposite is the case, and 70% of farmland in England is covered by agri-environment schemes.
“So it is nonsense for the RSPB to blame intensification for the problem. It is a pity they have once again gone for the knee-jerk reaction rather than look at the real reasons.”
Gavin Siriwardena, the BTO’s head of land use, said there was “no evidence” farming was responsible for the recent fall in kestrel numbers.
“Historically, it has always been a knee-jerk reaction to blame farming for any decline in bird numbers,” he said. “More recently, agri-environmental farming schemes have generally prevented bird numbers from falling.”
But Mr Siriwardena said farmers must increase their land use options, such as in-field management options, if they really wanted bird numbers to increase.
The BTO survey was not all bad news for birds of prey. Buzzards that thrive on rabbits and worms have increased by 63 per cent since 1995 and are now the most common sight by motorways. Red kites, tree sparrows and goldfinches are also increasing.
The British Breeding Bird survey involved more than 2,500 volunteers surveying 3,200 sites across the UK during the summer to monitor more than 100 bird species.
Bird numbers increasing in the UK since 1995, according to BTO
• Buzzards – 63% up
• Tree sparrows – 55% up
• Goldfinches – 56% up
• Bird numbers decreasing since 1995, according to BTO
• Yellow wagtail – down 52%
• Turtle dove – down 70%
• Grey partridge – down 50%