What's more, the decline of this, one of our closest human companions - according to Denis Summers-Smith, the acknowledged world expert on sparrows - may be, like the canary's signal of deadly gas for miners, a warning against the kind of lifestyle that we have adopted.
Anecdotal accounts of house sparrows plummeting in numbers have become commonplace. There have even been questions in the House of Lords - a measure of just how familiar and dear these perky little birds are to most of us. However, only now do we have enough facts and figures to back up this concern - as well as expert opinion about what's causing their decline.
From sample surveys taken across Britain in the Fifties, Denis Summers- Smith estimated that there were four to seven million pairs of house sparrows. By the late Eighties, based on information collated by the British Trust for Ornithology (BTO), he estimated that house sparrows had dropped by almost 50 per cent: to between 2.6 and 4.6 million pairs. All the evidence suggests a further, substantial, drop since then. However, most of the fall seems to be in sparrows living in the country and in city centres. Ironically, it's in that in- between sparrow territory we call suburbia, where the birds generally seem to be holding their own, whereas the large winter flocks that once noisily swarmed from one stubble field to another have almost vanished. Gone, too, are many of the city birds that used to set up their chirping homes in all manner of buildings.
BTO surveys of house sparrows on different types of British cultivated land spell out the difference. In rural gardens all over Britain, average sparrow numbers fell from 20 in the Eighties to nine in 1993, and have fallen further since.
The decline in rural sparrow populations is underlined by extra winter censuses in the mixed farmland to be found around Banbury in Oxfordshire. Compared with the first counts, in 1975, house sparrows have declined steadily ever since. By 1996, their numbers were halved. By contrast, suburban gardens seem still to be a haven for sparrows: the same period shows hardly any fall in numbers there at all.
It's possible, however, that sparrows have been in decline over a much longer period. This suggestion comes from autumn bird counts which have been made in Kensington Gardens in London since the early part of this century when there was a steep fall between 1925 (2,603 house sparrows) and 1948 (just 885). Denis Summers-Smith attributes this to the internal combustion engine which was then taking over from horse-drawn vehicles.
Why? Because piles of horse dung were an excellent source of insect food and seeds for quick-eyed sparrows. So, too, were the frequently spilt oats that were carried on cart and wagon to feed the horses.
Horses or no horses, the sparrow population has fallen far more since. By 1995 there were just 81 sparrows counted in Kensington Gardens, a measly 3 per cent of the 1925 population. Even more worrying, their decline has actually accelerated in the last two decades.
No one can be sure whether such city declines are mirrored elsewhere. But experts such as Summers-Smith are receiving anecdotal reports of falls not just in other European countries, but in North America too.
So why are sparrows in trouble? Summers-Smith rules out disease and the impact of increasing number of domestic cats or of wild birds of prey, simply because there is no evidence. Likewise he rules out city centre competition with pigeons and a lack of urban nest sites.
"In the country populations I'm convinced it's a decline in insects, which are essential food for young sparrows for at least the first three days of their life," comments Summers-Smith. "Modern intensive farming which uses pesticides, and the ploughing up of plant-rich places which used to support many insects, has done enormous damage. In urban areas, pollution is likely to have caused similar losses in insect feed," he adds. There has also been a decline in vegetable food, including grain, on which the adult sparrows feed.
Less food is scattered for chickens because most of them are no longer reared outdoors. Cutting fields for silage not hay, and ploughing-in stubble rather than leaving it all winter, have reduced the scatter of flower and grass seed - and cereal grain - that once gave succour to flocks of sparrows that could be a thousand strong.
Suburbia is different. More variety of habitats means more variety of grub. Bird feeding - a British obsession - helps as well. And a plethora of houses and outbuildings makes it easy to find nest sites. It may be why there's a theory - originally put forward to explain a similar sparrow anomaly in The Netherlands - that rural and city centre populations rely on immigration from the more productive suburbs to keep their numbers up.
Summers-Smith backs the theory. But of more concern to this retired consulting mechanical engineer - who has studied sparrows for more than 50 years and written many books on them - is what this decline in one of our closest companions should be telling us. His overwhelming conclusion is that - if over-intensive farming, copious pesticides, and an urban environment blighted by traffic fumes, has done for the sparrow - then it is quite likely do for us, too.
Duff Hart-Davis is awayReuse content