More than 50,000 birdwatchers are to take part in one of Britain's biggest bird surveys.
The survey should show whether conservation work is a success
Over the next four years, the British Trust for Ornithology aims to carry out a national stock-take of more than 250 species of British birds.
It aims to understand how recent changes to climate and habitats are affecting bird populations.
Results will be compiled in a winter atlas and will inform conservation work for the next 20 years.
The last ornithological study on this scale took place 20 years ago.
For the purposes of the survey, the UK will be divided into 4-sq-km areas of research.
In some areas, local birdwatching clubs will produce more detailed county atlases to complement the national picture.
Spotted a kingfisher?
It is hoped the information gathered will answer a number of conservation questions including whether birds are spreading north because of climate change.
It will also attempt to discover whether conservation programmes for species like the barn owl are working and whether birds such as the willow tit and hawfinch are extinct in some areas of the country.
BBC environment correspondent Sarah Mukherjee said project organisers were certain every one of the 50,000 amateur and professional birdwatchers would be needed.
She said they were also asking members of the public to play their part whether by spotting a sparrow in the garden or a kingfisher when out on a walk.