Authoritative work on species of hornbill wordwide. Specimen of juvenile female Tockus nasutus dorsalis collected by Fleck and stored in the Berlin Museum is identified by the author as the forementioned race, whereas a specimen from Maun is considered by the author to be T. n. epirhinus, even though it is not quite as dark as birds from Zimbambwe and Transvaal. Adult male Tockus erythrorhynchus ngamiensis collected by Roberts in Transvaal Museum, Pretoria, specimen No 17356.