The number of house sparrows in some urban areas may have fallen catastrophically, according to preliminary findings of the first official investigation into the decline of Britain's most common bird.

The number of house sparrows in some urban areas may have fallen catastrophically, according to preliminary findings of the first official investigation into the decline of Britain's most common bird.

The Government-funded study has found that up to 80 per cent may have disappeared in recent years, a phenomenon first highlighted by The Independent. Reasons for the fall in numbers are still unknown.

Nigel Clark, the head of projects at the British Trust for Ornithology at Thetford, Norfolk, said it was still too early to be sure of the scale of the decline but early analysis of the first data from the 18-month study suggested it could be highly significant.

"The early indications are that the population has declined by different amounts in different parts of the country," Dr Clark said yesterday. "In some urban areas we have seen quite a dramatic decline and it could be as high as 70 to 80 per cent, but I cannot be more precise as these really are very early indications."

The study, funded by the Department for the Environment, Food and Rural Affairs, has been looking at the populations of both house sparrows and starlings, once considered to be virtually immune to changes in farming practice and urban life.

Anecdotal reports of fewer house sparrows in cities and towns will now be followed up by a more rigorous scientific assessment based on past surveys of ringed birds.

Scientists will also study amateur sightings using the trust's garden feeding survey, where bird watchers are asked to keep records of the types and number of birds visiting their gardens each day.

One important aspect of the the department's study is to identify the "weakest link" within the sparrow's life cycle, which could identify for instance whether females are laying fewer eggs or fewer youngsters are surviving the first critical year of life.

There are several theories to explain a possible decline in the British house sparrow, ranging from an increase in predators such as sparrowhawks and cats, to the rise of pesticides and home improvements, leading to fewer nesting sites.