First they disappeared from Britain. Now Europe's house sparrows have vanished

The sparrow, once the exemplar of a commonplace bird, is becoming increasingly rare in France and other European countries.

The fall of the house sparrow (Passer domesticus) has already been well documented in Britain, partly thanks to a campaign by The Independent.

French ornithologists have now charted a steep decline in Paris and other French cities. There has been an even sharper fall in urban populations in Germany, the Czech Republic, Belgium, the Netherlands, Italy and Finland.

As in Britain, where sparrow numbers are believed to have fallen by 90 per cent in the past 15 years, continental ornithologists can find no coherent explanation for the sudden decline.

The mystery is especially deep in Paris, which is believed to have lost 200,000 sparrows - maybe one in 10 of the population - in the past 17 years. At the same time, the presence of somewhat more exotic "country" birds in the capital - from blackbirds to jays, kestrels and swifts - has increased.

The city's Muséum d'Histoire Naturelle is so concerned that it has launched a campaign to capture, examine and ring Parisian sparrows to investigate possible causes for their falling numbers.

"Is it a question of some form of disease or diseases? Or are their habitats being eroded? We hope to try to answer these questions," said Frédéric Baroteaux of the museum's research centre on bird populations.

The flocks of moineaux or "piafs" which flutter over all public spaces in Paris are part of the identity of the city. The diminutive singer Edith Piaf, who started as a street performer singing for "crumbs", took her stage name from the colloquial Parisian word for sparrow. Unlike in London, they remain familiar in Paris, but they are far less numerous than before.

Possible explanations have been offered by ornithologists. The rise in numbers and variety of other birds may have reduced their nesting places and feeding opportunities. And tightened building regulations, along with better maintenance, may have closed up the cracks in which they used to nest.

The number of Parisian cats is also booming, so they may be preying more on the birds. Some blame radio waves from mobile telephones or pollution from cars; but why should that affect sparrows and not other birds?

A similar pattern is reported across Europe. Hamburg estimates it has lost 50 per cent of its house sparrows in the past 30 years. In Prague the comparable loss is 60 per cent.

Alain Bougrain-Dubourg, president of the French equivalent of the RSPB, the Ligue de Protection des Oiseaux (LPO), says he fears the moineau may be on the same, steep downward flight path as the British sparrow. "All the signals are on red," he said. "The house sparrow is a highly symbolic bird, which has co-habited closely with man for 10,000 years. It may be less attractive than a blue tit but it has the right to survive, for the sake of biodiversity if nothing else."

The natural history museum has set up 10 sparrow ringing centres in the French capital and its suburbs. Birds are trapped in nets. Samples of blood and feathers are taken and examined for signs of disease or pollution. The sparrows are released with colour-coded rings on their legs.

The rings are needed because sparrows are wily birds. Once trapped in a net, they can not easily be caught a second time. The coded rings enable ornithologists to identify individual birds, and monitor their progress.

The bird protection league is also appealing to Parisians to place a sparrow nesting-box on their balconies amid their geraniums - and to keep their cats indoors.

The mystery still stands

Six years ago, The Independent began highlighting the decline of our most familiar bird. The campaign put the disappearance of the house sparrow on the national agenda. Abundant until the early 1990s, Passer domesticus has now gone from central London, apart from isolated pockets, and declined in other large urban centres, such as Glasgow. The cause is unknown. Our £5,000 prize for the first convincing scientific explanation stands, although many theories have been put forward, including magpies, cats, pesticides, peanuts, climate change and home improvements. Research by Dr Kate Vincent of De Montfort University suggests a decline in insects is leading to sparrow chicks starving. The effect is seen in Paris and across Europe.

The Independent's £5,000 prize is for a paper in a scientific journal. It is judged by our referees (the RSPB, the British Trust for Ornithology and Dr Denis Summers-Smith)