In a unique new collaboration, Collins have paired up with the respected British Trust for Ornithology, bringing together the most authoritative and up-to-date information in this new field guide to the rare birds of Britain and Ireland. This book is the companion volume to the Collins BTO Guide to British Birds. It covers all the rare and scarce birds that have occurred in Britain and Ireland four times or more, as of February 2015. `The Rarest of the Rare' section lists all the species that have occurred fewer than four times; taken in combination, this means that every species of wild bird that has ever occurred in Britain is mentioned. Species descriptions comprise the bulk of the book, and the text and photographs describe and illustrate the key features needed to identify these birds with confidence. Confusion species are included, as are vocalisation details for species whose identification it aids. The photographs have been chosen carefully to show key features that are described in the accompanying text; they also give clues to the usual habitat favoured by the bird and its typical posture. Many of the photographs are seen here for the first time. `ID Key Feature' pages provide a quick guide to a group of species or families; they describe the structural and behavioural features that an observer should concentrate on initially when they come across an unfamiliar bird. Where relevant, these feature pages also highlight identification pitfalls. Unlike its companion volume, distribution maps are not included, as they are of little relevance when dealing with rare and scarce birds in Britain and Ireland: by their very nature, vagrant birds can turn up almost anywhere. However, where a part of Britain or Ireland is noteworthy for the occurrence of a given species, then the region in question is mentioned in the text.