Help solve London's great sparrow mystery

A City-wide audit of London's house sparrow population began yesterday in the latest attempt to discover the reasons behind the dramatic fall in their numbers in the capital.

A City-wide audit of London's house sparrow population began yesterday in the latest attempt to discover the reasons behind the dramatic fall in their numbers in the capital.

The survey, one of the biggest studies of its kind, will try to discover the small urban pockets where the house sparrow continues to thrive and the places from which it has disappeared. Conservationists will try to resuscitate the species and unravel the continuing mystery of its decline.

The reasons remain unclear but the sparrow's tribulations are not limited to the cities where it is most marked. In 1925, 2,603 house sparrows were recorded in Kensington Gardens, west London, but so far this year there have been only four.

The work of ornithologists with the much less common tree sparrow has shown that extra feeding can bolster the population, a tactic likely to be adopted in the capital, says the London Biodiversity Partnership which is behind the study.

In some parts of the country up to 80 per cent of sparrows may have disappeared in recent years. From a time when thousands of them lived in urban areas, the Isle of Dogs in east London is now known as a population pocket in the capital but with only 30 to 40 pairs.

The survey is encouraging thousands of people to report the numbers – or lack of them – of house sparrows across all areas of the capital.

Chris Packham, the president of London Wildlife Trust which is part of the new initiative, said: "Ornithologists are telling us there are four pairs at the Tower of London. Four pairs of kestrels would be mildly interesting but this symbolises the state of this once-familiar bird. I can't help feeling a little guilty it has slipped through our fingers."

Different studies are being done across Britain to establish the best conditions for sparrows to survive. New towns with a large number of modern industrial units do not provide the crumbling brickwork in which sparrows like to nest, and in some places ornithologists have provided nesting boxes.

Despite a wide variety of reasons for the decline, no authoritive study has yet been published – despite an offer of £5,000 from The Independent – to explain the phenomenon.

Birdwatchers reported a total of 673,000 sparrows in a mass survey earlier this year, which showed a drop of 57 per cent in their numbers since 1979. Other European countries have also noted declines in the sparrow population.

Educated guesses have pointed to additives in unleaded petrol, the rise of pesticides, and a knock-on effect from the tribulations of the rural sparrow population. The bird is now on the official "red list" of species of conservation concern.

To take part in the study, go to www.rspb.org.uk