By Sarah Mukherjee
BBC environment correspondent, Norfolk
The biggest bird survey ever to take place in Britain started on Thursday.
The survey should show whether conservation work is a success
The four-year project, being organised by the British Trust for Ornithology (BTO), will involve more than 50,000 volunteers, who will record every bird they see.
The resulting map will provide a comprehensive picture of the nation's bird life, and will be used in research.
On my visit to eastern England, you could see why the British autumn has inspired so many poets and artists.
A clear, cobalt-blue sky was suffused with gentle golden sunshine. The trees surrounding the BTO's headquarters in Thetford in Norfolk seemed almost luminous, with colours ranging from pale lemon, through vibrant oranges and reds, to russet brown.
But it was not the trees, beautiful as they were, which we had come to see.
The BTO's Graham Appleton handed me a pair of binoculars, and pointed out the robins, crows and a jackdaw making a nest in one of the organisation's chimneys (somebody's going to have a cold winter in the office this year).
We were forming a small part of the biggest ornithological survey ever to take place in Britain.
Every square mile of the country, from fashionable inner city canal-side parks to wild, open Scottish mountainsides, from suburban back gardens to Cornish coastal coves, will - it's hoped - be mapped for the birds they contain over the next four years. Suddenly, 50,000 volunteers doesn't sound like a lot.
"The last time we did this was 20 years ago," Graham said. "We want to find out exactly what is happening to the bird population."
We were joined by the organisation's enthusiastic new director, Andy Clements. Aren't people a little sceptical about these exercises these days, I asked him? All that filling in forms online - won't a lot of them end up in the virtual bin?
"Not at all," Andy said. "The last map we did like this was in the eighties, and the government based its strategy for farmland birds on the map from then on. It really does matter, and we want to hear from anyone, anywhere, anytime, who's seen a bird so the map will be as comprehensive as possible."
Next, we were off to see one of those volunteers. Jan Toomber lives on the edge of Thetford forest, in what even she describes as a "gingerbread house".
Spotted a kingfisher?
"People always go 'ahhh' when they see it," she added with a smile. Behind her, a patchwork of native broadleaved trees and conifers glowed in the sunlight.
She reeled off the birds she'd seen in the last hour or so - robins, woodpeckers, crows - even tawny owls at night. All very well if you live in an area that a Hollywood director could use as a set for Hansel and Gretel - but what about if you're in a city flat, where the only green space is a distant park?
"It doesn't matter," Jan said. "We really need that information, because often people spot birds, but don't report them in areas like that because they don't think it's important. But it is - and once you start, it's really fun."
Jan admitted she now rarely leaves home without her notebook. You don't have to be a committed birder like Jan; but if you want to have a go, the BTO website will tell you how. And, it must be said, such is the infectious enthusiasm, you do find yourself making a mental note when you come across one of our feathered friends about their business.