Chorus of concern for songbirds

It is an hour before dawn, and in the dark of a suburban garden the sounds of sex and violence are echoing. As the light grows, dim shapes can be seen flitting through the shrubbery.

"That's a sparrow," said Alan Bender of the West London group of the RSPB as a soft cheeping emerges from under a tangled briar. One of the country's leading experts on birdsong, he is surprised: in a four-day survey of London's dawn chorus, this is the only "common" house sparrow to be either seen or heard.

Even 10 years ago, the sparrow was ubiquitous. Now it is in drastic decline and next month the RSPB is hoping Londoners will help it carry out a major survey to find the sparrow's remaining strongholds.

According to the RSPB's annual snapshot of bird populations, the Big Garden Birdwatch, in 1979 there were an average 10 sparrows seen in each London garden during an hour of one weekend in January. In 1991 it was 8.7, in 2001 it was four, and this year it was just 2.43. That is a 75 per cent crash in 23 years.

Another familiar voice is missing. Not long ago, the mellifluous repeated phrases of the song thrush were more or less routinely heard. Now the song has vanished from many former haunts, London squares among them, in a national population crash of 70 per cent in 30 years.

Song thrushes are still present in London, but mainly in parks and gardens. The one example in the city centre - in Belgrave Square - was seen and not heard. The Evening Standard carried out a survey of the dawn chorus in three different London cityscapes. We found 15 species singing in a suburban garden specially prepared to attract wildlife, and 17 singing on Hampstead Heath. Heron, woodpecker, and even the blackcap, a migratory woodland warbler, join more usual blackbirds, robins and wrens. In Belgrave Square, a private square in the heart of Westminster, 11 species sang. Around 25 species might be expected in a chorus in rural ancient woodland. "Listening at dawn is a good indicator of what birds are around and are breeding, but it is just a snapshot," Mr Bender said.

Our survey confirmed the variety of species in the chorus, and the sheer number of birds, grows in proportion to the amount of undergrowth about. It is also heavily dependent on the abundance of insect life. This can be encouraged by wildlife-friendly gardening such as encouraging a few "weed" species of plant, not using insecticides, providing water, and allowing some wood to lie about and rot.

The poorest choruses were in open, public squares with no undergrowth, a formal layout, and few native species of tree. Berkeley Square was the one no-show: nothing sang, let alone a nightingale.