Number-crunchers will make sense of a century of surveys

The forthcoming investigation into the decline of the house sparrow, to be announced by the Government today, is partly to be a giant number-crunching exercise - one of the biggest ever carried out in the world of ornithology.

The forthcoming investigation into the decline of the house sparrow, to be announced by the Government today, is partly to be a giant number-crunching exercise - one of the biggest ever carried out in the world of ornithology.

It will involve extensive analysis of several of the large long-running surveys which make Britain's birds the most closely monitored in the world.

Six surveys in particular will be examined by computer for evidence of patterns of decline in sparrows in towns, suburbs and the countryside, and for similar declines in starlings. Some of them are confusingly similar (except to experts) but all give valuable information.

The oldest is the National Ringing Scheme, which dates back to 1908. Recoveries of ringed birds can give data on their movements and on how long they live: there are thought to be records on 400,000 sparrows that have been ringed and about 6,000 that have been recovered.

The Nest Records Scheme, started in 1939, gives information on numbers of eggs, egg-laying dates and how successful are different broods. It is done for more than 200 species and involves about 40,000 records a year. Currently, about 250 house sparrow nest records are being received annually.

The Common Bird Census, which started in 1962 and ends this year, is a territorial mapping exercise which indicates how many birds are in a given area and is done on 300 countryside plots across Britain. It has many thousands of sparrow records, as does its replacement, the Breeding Bird Survey, which covers 2200 plots much more randomly chosen, some of them in urban areas.

Suburbs and towns are covered by The Garden Bird Feeding Survey, which goes back to 1970 and covers 200 gardens across Britain, and the much more extensive Garden Birdwatch, which began in 1995 and has 13,000 contributors.

Dr Humphrey Crick, the British Trust for Ornithology scientist leading the enquiry, said: "We have millions of pieces of data and what's good is that much of it is very long-term. We're going to combine the information and interrogate the data sets to see how and where things have changed and what the factors affecting the birds are."