Of the 36 species on the list published yesterday, 23 have had their UK populations halved or more over the past quarter century. Ten years ago there were only eight species in this category.
``Things are getting worse rather than better,'' said Dr Mark Avery, chairman of the Birds Conservation Group which agreed the list. ``The fate of these birds acts as a barometer of the health of the environment.''
The eight conservation organisations which drew up the list believe modern farming methods are to blame for several of the species' declines. Nine farmland birds - the turtle dove, skylark, song thrush, spotted flycatcher, tree sparrow, linnet, bullfinch, reed bunting and corn bunting, have all been added since the last published list six years ago.
The move from spring- to winter-sown cereals, neglect and grubbing out of hedgerows and the use of pesticides are thought to be the major causes of the birds' difficulties.
Some of those on the list are extremely rare - the bittern has only about 20 breeding pairs in the country. Several hundred red-backed shrikes bred in Britain 30 years ago, but now, in some summers, the shrike raises no young here. At most only a handful of pairs breed.
The red list also contains species whose numbers still run into hundreds of thousands but are falling very rapidly. Worst hit is the tree sparrow, which has seen a population decline of 89 per cent in 25 years.
Dr Avery fears that when the next red list is drawn up in five years time more species will be added. ``We have an amber list of 110 species found in Britain which we say are of medium concern," he said. "But among those there are several candidates for the next red list.''
The lists were agreed by the Royal Society for the Protection of Birds, the British Trust for Ornithology, the Wildlife Trusts, the National Trust and four other conservation organisations. The groups looked at data for some 300 species which breed or winter in these islands, and decided that almost half gave grounds for concern.
Red-list birds were those whose population had at least halved in 25 years, had suffered a long-term population decline in the past two centuries, or where the global population was now very low and Britain was home to a large part of it.
The conservation organisations say that with the right research, policies, incentives and cash backing, the declines can be halted and species brought back from the brink; numbers of breeding corncrakes, for example, have risen for the past two summers in the Scottish islands.
Conservationists are asking children to forego the seasonal delights of collecting frog spawn and watching tadpoles grow in jam jars. Frog and toad populations are believed to be in decline in Britain and across most of the globe, with habitat change, pollution and disease thought to be the main causes.