Bird Atlas (and my legs)
As the name suggest, this amazing book of over 700 pages and weighing in at over 3kg (according to one tweet I read, I haven't weighed it, honestly), is the result of 4 years of fieldwork by over 40,000 volunteers (myself included, see posts here), throughout the UK and Ireland, and provides an overview of the breeding and wintering status of all British birds. There are some good news stories, but unfortunately, also several worrying statistics, charting severe declines for many species.
I've just had a quick flick through, but I'm very pleased to see that my patch, Linacre Reservoirs, gets a special mention on p.190, in the section about Mandarin Ducks.
To take a look for yourself and to order a copy, follow this link.