Cuckoos occur in a wide range of habitats from open savanna to dense tropical forests, and from sea level to 4,300m in all parts of the world except the Polar regions. The 144 species in this book include not only the typical arboreal cuckoos that most of us are familiar with, but also ground cuckoos, roadrunners, coucals, couas, malkohas, lizard cuckoos and hawk cuckoos - in fact birds measuring from about 15cm to 70cm in total length, and from 14.5g to 790g in mass.
This book is the latest in a long line of Helm Identification Guides and (like that on Cotingas and Manakins) breaks from the tradition of a white cover. Every species is illustrated across a series of 36 colour plates towards the front of the book by Richard Allen, Jan Wilczur, Martin Woodcock and Tim Worfolk. These are of perched or running birds showing both adult and juvenile plumages and significant races. Later in the book each species has a detailed account spanning up to four pages. This includes an excellent multi-colour map, and usually several colour photographs - of which there are over 350 in total. The text covers all aspects that you would want to know such as taxonomy, field identification, description, biometrics, moult, geographical variation, distribution, habitat, behaviour, breeding, food, status and conservation. A number of these subjects are also dealt with in a 12 page overview at the beginning of the book. There is also an extensive bibliography of over 2500 references and a short glossary.
As is often the case in such books, the authors' opinions on taxonomy differ to some of the major checklists - Clements recognises just 142 species while the IOC lists 149. For the most part they have accepted the genera and species limits set by Robert Payne in his book The Cuckoos (OUP, 2005). That book recognised 140 species, and this one adds four others - Scaled Ground Cuckoo (split from Rufous-vented Ground Cuckoo), Gould's Bronze Cuckoo and Pied Bronze Cuckoo (both split from Little Bronze Cuckoo), plus Rusty-breasted Cuckoo (split from Brush Cuckoo). Keeping in line with Payne they lump Andaman Coucal into Greater Coucal (although this is widely recognised as a split by many) and Burchell's Coucal into White-browed Coucal (split by birders in southern Africa, but lumped by many others), while Pacific Koel is absorbed into Common Koel, which is given a total of 18 subspecies.
What comes across clearly in the text is that this is a fascinating group of birds. For example, cuckoos exhibit the full range of breeding systems. Some are brood-parasites, others rear their own young, while at least one does both! Some are co-operative breeders, some are monogamous while in other species a male might mate with two females, or a female may be served by two males. An interesting fact is that brood-parasitic cuckoos have smaller brains than those that make their own nests. It is perhaps not surprising that with all this variation many biologists have chosen cuckoos for their research.
If you already own Robert Payne's book you will find much of the same material here - but with better maps and illustrations, and plenty of photographs to make it a worthwhile purchase.