Keith Vinicombe 
Helm Guide to Bird Identification [PDF ebook] 

An essential field guide companion covering species pairs or groups that are difficult to identify. This book covers difficult identification issues by looking at tricky species pairs or groups of birds, and comparing and contrasting their respective features. Designed as a field companion, it supplements the standard field guides and provides much additional information. As well as detailed texts, the books include extensive illustrations of all relevant ages and plummages of the species concerned.