In Europe, the case of the missing sparrows

Across the Channel, the French Bird Protection League is organizing a similar survey in Paris this spring, after local bird-watchers reported puzzling sightings. In one park, they found the same number of sparrow nests as there were 10 years ago. In another, the population has dropped by two thirds.

In both places, says bird-lover Christian Gallinet, who worked on the study, "the couples that we fed had no more than one or two young, when normally they should have three or four.

"Something odd is going on, and nobody has any explanation for it yet," he adds.

There are plenty of theories, though.

Some experts have suggested that as cities have protected their suburbs, prohibiting building, developers have turned their attention to inner-city wastelands, robbing sparrows of the overgrown, weedy areas where they typically forage for seeds.

Others wonder whether modern buildings lack the nooks and crannies that sparrows like to nest in. But that idea takes a knock in Holland, where birdwatcher Guus van der Poel found as he counted sparrows that "some city centers are sparrow-free, and in areas where the houses were built before 1953 there is a good chance there will be no sparrows at all."

Suspicion has also fallen on Felis domesticus, the house cat.

One study found that as many as 25 percent of sparrows in an English village fall prey to prowling felines. But cats have been hunting birds since time began, and though food shortages may have forced sparrows to take greater risks, it is hard to believe that predators could have halved the British sparrow population in 30 years.

A key problem, a number of experts agree, appears to lie in a shortage of the tiny insects that fledgling sparrows need during the first three or four days of their lives, before they move on to a vegetation diet. Mr. van der Poel blames industrial agriculture, which he says has robbed the countryside of the variety of flowers and weeds that insects need.

Summers-Smith points the finger at another culprit - unleaded gasoline, though he acknowledges that the evidence is only circumstantial. The catastrophic fall in urban sparrow populations began in 1990, he points out, one year after unleaded gas was introduced in Britain.

Unleaded gas contains unstable toxic compounds that Summers-Smith believes might be killing off the invertebrates that baby sparrows depend on. The fact that sparrows in Paris are doing better than their London cousins, he suggests, may have something to do with the fact that diesel fuel is much cheaper, and thus much more commonly used, in France than in Britain.

But he says his ideas are "highly speculative and highly circumstantial. This problem requires academic research."

Belatedly, perhaps, ornithologists are now turning their attention to the lowly sparrow.

"When I first started studying the sparrow just after the (Second World) War, most of my colleagues didn't think it worthy of even being called a bird," Summers-Smith recalls. "Now it is a high-profile bird."

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