Thousands of volunteers begin epic task of building atlas of our birds

Britain and Ireland's vast armies of amateur naturalists are being mobilised, starting this weekend, to undertake the awesome task of mapping and counting the two nations' wild bird populations.

It is the first time in two decades that the ambitious stock-take of the natural world has been attempted and experts believe the resulting bird atlas, to be published in 2012, will give the most comprehensive picture to date of the impact of climate change on species and the success of recent conservation efforts.

Tens of thousands of volunteers are being sought by the British Trust for Ornithology over the next four years so each and every corner of the British Isles is accurately audited.

The Independent is backing the project and urging readers to log on to the BTO's website at http://www.bto.org/birdatlas/taking_part/index.htm to find out how they can help set the agenda for bird conservation in Britain and Ireland for the next 20 years.

There are two ways of taking part. First, enthusiasts can record all the birds they can see over the course of one hour during four visits – two in winter and two in summer – to a specific 2km by 2km square on the map, an area also known as a tetrad.

Or second, those with a little less knowledge or confidence can join in by reporting one-off sightings, so-called roving records, such as seeing the distinctive blue flash of a kingfisher while out walking or hearing the late night hooting of an owl.

With more than a third of the UK's birds to be spotted in back gardens, organisers insist that anyone can join in.

Those taking part will be not be expected to be expert ornithologists but amateurs with a basic ability to identify key species and the commitment to help the environment. Professionals will be on hand to authenticate all the results.

Yesterday, as the sun poked through the clouds at Abberton Reservoir in Essex, lighting up the stunning autumn foliage along the water's banks, Dr Simon Cox, a retired GP who is co-ordinating the counting effort in his county, had totted up more than 40 species in his 60 minutes of observation.

"Not all habitats will be as rich as the one we have here but even in urban areas you can expect to see up to 20 species if you look hard," he explained.

With some 40,000 ducks, geese and swans thought to be present at the 1,200 acre reservoir, logging them all is no mean feat. In addition to the dozens of waterfowl, including a family of Bewick's swans fresh in from the Siberian tundra just a few days earlier, there were more familiar birds – chirping robins, swaying wagtails and great tits busy nibbling at the well-appointed nut feeders outside the Essex Wildlife Trust visitor centre.

Each is equally important to the final picture, he said, illuminating exactly which birds may be thriving and which others are struggling to cope with altered modern conditions.

"There is a lot of satisfaction to be obtained by knowing that you are contributing to something vitally important to birds as well as just the sheer pleasure of going out looking for birds on your local patch where inevitably you will make some unexpected discoveries," said Dr Cox yesterday.

The BTO expects to gather data on 250 species during the course of the survey, including 40 currently on the red danger list and 121 amber-listed because of conservationists' concerns for their future. Among the questions they will be asking is whether efforts to help barn owls are working, or if the willow tit and hawfinch are now extinct in some counties.

Another key issue is whether some of the country's bird species are spreading north seeking cooler climes because of global warming and the impact on breeding and migration times. Then of course there is the question of the continuing decline of the house sparrow.

Naturalists believe that bird numbers are a key barometer of how the natural world is coping from the pressures of climate change and habitat depletion.

Andy Clements, the BTO's director, said: "This is the biggest project that the UK's birdwatchers have ever undertaken. We have been making preparations for this survey for more than three years and now finally we are able to fire the starting gun."

Ten to look out for

* BARN OWL (Tyto alba): Has suffered 50 years of decline due to intensive agriculture but numbers now growing. Seen in open country or at field edges. Estimated: 4,400 pairs.

* WILLOW TIT (Parus montanus): Red-listed, this medium-sized tit is best spotted in willow thickets and boggy marshland.Estimated: 25,000 territories

* HAWFINCH (Coccothraustes coccothraustes): UK's largest finch, shy with powerful bill. Amber-listed. Most likely to be seen in west and Home Counties. Estimated: 3-5,000 pairs.

* TURTLE DOVE (Streptopelia turtur): Summer visitor noted for its gentle purr has suffered huge decline. Best seen in south and east on woodland edges. Estimated: 75,000 territories.

* COLLARED DOVE (Streptopelia decaocto): Rapidly spreading bird often seen in flocks where food is plentiful around gardens, parks and farms. Estimated: 210,000 territories.

* RAVEN (Corvus corax): Member of the crow family, bigger than a buzzard, distribution increasing. Best looked for in rugged upland areas. Estimated: 7,500 breeding pairs.

* BUZZARD (Buteo buteo): Most numerous bird of prey, once confined to western England. Seen perched on pylons or fence posts. Estimated: 44,000-61,000 breeding pairs.

* NIGHTINGALE (Luscinia megarhynchos): Secretive brown bird with beautiful song rarely found outside south- east England. Arrives in April.Estimated: 5-6,000 breeding males.

* KINGFISHER (Alcedo atthis): Unmistakable blue bird spotted swooping over rivers and watercourses. Amber-listed after recent declines. Estimated: 3-6,000 pairs.

* CORNCRAKE (Crex crex): Normally found in dense vegetation and famed for its rasping call. Now perilously few in number and confined to Scotland. Estimated: 600 calling males.