THE BIGGEST ever survey of British bird populations will begin next week using an army of 50,000 bird-watchers - most of them amateur volunteers - to chart the fortunes of some 250 species.

Bird numbers provide a barometer of how the natural world is coping with pressures from climate and habitat changes

Baroness Barbara Young - BTO President

Working with colleagues from Scotland and Ireland, the British Trust for Ornithology (BTO) will launch the census on November 1 to check the survival rates of some threatened species - there are 40 "red-listed" as being under severe threat and 121 "amber-listed" - and also to provide vital data on how global warming is effecting bird life.

The assembled data will provide ornithologists with enough data to create a British Isles bird atlas and recommend conservation measures for the next 20 years. It will also answer some key questions including:

• Is Barn Owl conservation working?
• Have Willow Tit and Hawfinch become extinct in some counties and regions?
• Are birds spreading further north as a result of climate warming?
• Where are the remaining breeding concentrations of Turtle Doves and Nightingales?

Writing in the National Bird Atlas appeal brochure, the BTO's President, Baroness Barbara Young of Old Scone, comments: "Bird numbers provide a barometer of how the natural world is coping with pressures from climate and habitat changes. Bird Atlas 2007-11 will deliver vital evidence for conservation practitioners."

On 1 November (and for the next four years) birdwatchers will be taking to the hills, tramping around fields, strolling through woodland or just reporting on the birds that visit their gardens.

They will record, count and seek out as many species as they can, to see just how much has changed since the last Winter Atlas (1981-84). Next summer they will search out breeding species, comparing their observations to the last Breeding Atlas (1988-91).

• The BTO is keen to involve as many birdwatchers as possible, however knowledgeable they feel they are. For more information, see www.bto.org/birdatlas