SOLVED The riddle of the vanishing sparrows

. . . and the reason for their disappearance from central London may have alarming implications for human health

The sudden disappearance 25 years ago of huge numbers of sparrows from the centre of London is one of the most puzzling environmental mysteries of recent times.

Once as familiar as double- decker buses, they simply melted away. From tourist hotspots such as Trafalgar Square, Piccadilly Circus and St James’s Park, to the great railway stations, which in the mid-eighties were thronged with them, sparrows are now marked by their absence.

Certainly, by the start of the millennium, although there were still pigeons galore, the sparrows in central London had gone. No one knew the reason.

Now a possible explanation is emerging. In a development as ominous as it is remarkable, there is evidence that air pollution — and, in particular, the noxious exhaust fumes from diesel vehicles which are causing more and more concern for human health — may be what did it for sparrows.

The evidence centres around sales of diesel vehicles in Britain since 1980 — a move encouraged by all governments until recently because they produce less climate-changing carbon dioxide than petrol- driven motors and were, therefore, regarded as more environmentally friendly.

The figures show a huge surge in the early Nineties, which correlates with the sparrows’ abrupt disappearance.

It finally suggests a potential trigger for a natural crisis which has been perplexing, because the house sparrow ( Passer domesticus) had always seemed like the ultimate urban survivor.

It is one of the world’s most successful creatures, occurring naturally across europe, much of Asia and North Africa, and has been introduced to Southern Africa, Australasia and the Americas (Washington and New York are full of sparrows). Antarctica is the only continent without them.

They’ve been found breeding 14,000ft up in the himalayas, and nearly 2,000ft underground (in Frickley Colliery near Doncaster, in 1979). They’re one of the world’s commonest birds and almost certainly the most widespread.

DOWN the centuries, the house sparrow has sparked a special warmth in humans, based on its close association with towns. This has given a perception of its character as humble but hardy, small but street-smart.

When hamlet told horatio, ‘there is special providence in the fall of a sparrow’, he was using it as an example of the lowly.

Yes, we think of it as an urchin, but an urchin that lives on its wits. If anything would survive whatever the modern city could throw at it, it was London’s Cockney sparrer. Yet it didn’t.

The rapidity was the most striking aspect of its demise.

Throughout the 20th century, house sparrows underwent a gradual decline, thought to be linked to the disappear by ance of the horse from London’s streets ( undigested grain in horse manure had been a major food source).

We have a good picture of that, thanks to the birdwatching activities of one of Britain’s most celebrated environmental figures.

Max Nicholson was a senior civil servant, who, in 1949, brought into being the world’s first statutory conservation body, the Nature Conservancy, and subsequently ran it for 15 years. he was one of the founding fathers of the World Wildlife Fund in 1961.

But he had also been, since his earliest years, a passionate ornithologist, and in November 1925, aged 21, he and his brother went to one of central London’s greenest parks, Kensington Gardens, and counted 2,603 house sparrows there.

Years later he returned to count again. In December 1948, there were 885; in November 1966: 642; and in November 1975 there were 544. A steady but slow decline. When he counted in February 1995, the numbers had dropped off a cliff: just 46.

And when, aged 96, he did his final count on November 4, 2000, almost 75 years to the day since his first, helpers from the London Natural history Society could find, in all of Kensington Gardens, but eight birds.

This rapid collapse is backed by records from other parts of the capital.

In Buckingham Palace gardens, the last birds bred in 1994; in St James’s Park, where, in the eighties, sparrows would swarm in fluttering flocks onto the hands of visitors holding seed, the birds had gone completely by 1999.

Around the early Nineties, then, something catastrophic suddenly began to happen in the ecosystem of the house sparrows of central London. But what?

It has remained one of Britain’s most baffling environmental events, though when the disappearance at last became properly appreciated by the public, from the year 2000 on, many reasons were put forward, some more sensible than others.

They ranged from pesticides to peanuts (supposedly poisonous in bird- feeders), from climate change to the Chernobyl nuclear disaster, and from home and garden improvements (loss of green spaces and nest holes) to predators such as magpies, sparrowhawks and cats.

But while some of the above may have influenced numbers or behaviour, scientists of the Royal Society for the Protection of Birds and the British Trust for Ornithology didn’t think any of them were actually driving the decline.

The world expert on sparrows, Denis Summers-Smith, had a different idea; he thought the reason might be to do with air pollution. A former ICI engineer, Dr Summers-Smith has spent a lifetime studying the house sparrow, and all the other members of the sparrow family.

he thought it possible that introducing leadfree petrol in the Nineties might have affected the birds, because of a potentially harmful chemical in the new fuel. But this could never be proved

Over the years, Dr Summers-Smith modified his view. he began to think the problem might be exhaust gases from diesel vehicles, and specifically their microscopic soot particles — particulates — now seen as a major health hazard for humans and cause of respiratory problems.

It is thought they may be responsible for 29,000 premature deaths a year in Britain. They might be responsible for sparrow deaths as well, he thought.

Talking to him about this recently, I realised he had never put together the picture of the uptake of diesel in Britain (he is 97 now, though still very active).

SO I sought the figures from the Society of Motor Manufacturers and Traders — and I was taken aback.

The mysterious plunge in numbers in London’s sparrows in the Nineties is clearly matched by a corresponding surge in the uptake of diesel vehicles in Britain.

Diesel registrations doubled between 1985 and 1990 from 64,000 to 128,000, then they leapt to 200,000 in 1992, 340,000 in 1993 and 431,000 in 1994.

The resultant air pollution will have been greatest in towns and cities, and greatest of all in London, where urban air pollution is worst.

In other words, harmful diesel particulates in the air in the capital will have increased substantially just before its sparrow populations began collapsing.

Let us admit this is a correlation, not causation. But the parallel is striking. Dr Summers-Smith feels it is convincing. ‘I think it is the smoking gun,’ he said.

Only in recent years have we begun to appreciate the seriousness of the threat of diesel pollution. Now, potential health damage from particulates and oxides of nitrogen is seen as outweighing the benefit from less CO2. Thus, an effective national urban air pollution policy is becoming an ever more urgent need.

Two months ago, the Government was told by the courts for

the third time that its efforts in this area were inadequate.

Today, we know, all too well, that diesel can be deadly.

however, it would be ironic if, just as coal miners had their canaries to warn them quickly of noxious gases underground (by expiring), we had a modern-day version of the miner’s canary in the house sparrows of central London. But that we did not begin to recognise what their disappearance was telling us until 25 years after the event.

Michael Mccarthy is the author of the Moth Snowstorm: Nature and Joy.