What is killing our sparrows?

Pesticides, peanuts, climate change, the Chernobyl disaster, front gardens turned into car ports, loss of privet hedges, home improvements, lead-free petrol, cats (oh yes, cats!) sparrowhawks... but most of all magpies. These are among the reasons put forward by Independent readers for the sudden disappearance of the house sparrow, in the flood of letters we have received since we began our campaign last week to save what until recently was our most commonplace and familiar bird.

Pesticides, peanuts, climate change, the Chernobyl disaster, front gardens turned into car ports, loss of privet hedges, home improvements, lead-free petrol, cats (oh yes, cats!) sparrowhawks... but most of all magpies. These are among the reasons put forward by Independent readers for the sudden disappearance of the house sparrow, in the flood of letters we have received since we began our campaign last week to save what until recently was our most commonplace and familiar bird.

The magpie, the striking black and white member of the crow family which in the past 25 years has moved from the countryside into the towns with unstoppable success, is so far chief villain. Numerous readers blame its aggressive predation on small songbirds - which they have often witnessed - for the disappearance of sparrow colonies from their gardens or neighbouring parks.

But there are a wide range of other theories, befitting the large correspondence we have received - 142 letters since 16 May from all over Britain. There is not remotely enough room - alas - to publish them in full but all have been carefully analysed.

They come from towns and cities, from suburbs and from deep in the countryside, and their writers have ranged from pensioners in their eighties to the children of Lewis St County Primary School in Eccles, Greater Manchester, who are now beginning their own project on the sparrow's decline.

Some of the letters - happily - tell us the bird is flourishing in the writer's locality. These include Seaford and Hastings in East Sussex; Herne Bay, Kent; Malmesbury, Wiltshire; Wantage, Oxfordshire; Huntingdon, Cambridgeshire; Market Rasen, Lincolnshire; Chester, Cheshire; Bury, Greater Manchester, Barnsley, south Yorkshire; Harrogate, north Yorkshire; Cramlington, Northumbria; and Perth. Researchers might like to note the preponderance in this list of market towns and seaside localities.

But far, far more readers tell us of the house sparrow's disappearance, often sudden, and often in the 1990s; in so far as any critical year is indicated, it appears to be 1997. WroteGranville Bantock, of Hampton, Middlesex, whose long-established garden colony of 30 sparrows disappeared abruptly that year: "During the summer when travelling 60 miles to our caravan in Kent, we noticed that not one insect was stuck to the windscreen... during every preceding year we were unable to travel the 60 miles without the windscreen being 'plastered' with insects. We guessed that something catastrophic had happened..." Had it? Time, and research, will tell.

What characterises the letters and makes them valuable and indeed moving, is the wealth of such observation, and also the passion with which people lament something so seemingly inconsequential as the absence of a small brown bird. It's as if a floodgate has been opened: a commonly expressed feeling is thanks to The Independent that someone besides the writer has at last noticed this and also thinks it's important.

There are dozens of theories for the sparrow's disappearance but a few clearly stand out. The magpie is top of the list. The Royal Society for the Protection of Birds and the British Trust for Ornithology insist research shows the increase in magpies is not linked to the decline in songbirds: many people do not believe it. They have seen these large, bullying crows arrive in their gardens and kill young sparrows by the nestful, as well as many other small birds. Seventeen readers blame the magpie directly.

Sparrowhawks, which in the 1990s have had a similar urban population explosion to the magpie - they are now found in many suburbs - are not far behind, and the third predator people widely blame is the domestic cat, often with a depth of feeling that would make any cat lover wince.

More subtle reasons advocated by numerous readers include the massive increase of poisonous pesticides in gardens, meaning a great loss of insect food; and the loss of garden green space and hedges to car ports and conservatories, and the increase in loft insulation and home improvements generally, which deny sparrows nesting places.

More unusual theories advanced include the possibility of poisoning from the peanuts increasingly used in bird feeders (five readers), and the ill-effects of the cloud of radioactive dust from the explosion at the Chernobyl nuclear reactor, which passed over Britain in the spring of 1986 (two readers).

Two very suggestive theories have been put forward among the less common ideas. One, from three readers, is the introduction of lead-free petrol in the 1990s, and the possibility that the additives included in it to make up for the loss of lead might have a harmful effect either on insects or the birds themselves; this would certainly parallel their decline. The other is the general "tidying up" of houses and gardens which has left nesting places in short supply.

The truth may be in there somewhere. We shall keep you informed.