Owls of the world - Claus Knig

Owls are enduringly popular birds, but due to their nocturnal habits

most species are difficult to see well. The plumages of many species

are cryptic and difficult to separate by plumage alone. This problem is

compounded by the different morphs that many adopt. This book fully

describes every known species and subspecies of owl, as well as

presenting the latest evidence on owl taxonomy, based on DNA work and

vocalisations. Because voice is vital in owl identification, much

emphasis is placed on it in the book and sonograms are provided for

many species.