The Plain-pouched Hornbill Aceros subruficollis has been the subject of considerable taxonomic
confusion (reviewed herein), but is now considered to be a full species. Originally known only
from southern Myanmar (Burma), it has also been thought erroneously to occur in north-east
India, north and west Burma, north-west Thailand, Sumatra, and Borneo. Most of the confusion
is due to the similarity of adult Plain-pouched Hornbills to juveniles and the Greater Sunda
populations of the Wreathed Hornbill A. undulatus. Numerous morphological characters, however,
differentiate the species, and these are described and illustrated in this paper. Its true range evidently
includes only southern Burma, south-west and southernmost Thailand, and northernmost
Malaysia. Although this re-evaluation of the species’s range shows it to be a great deal more
restricted and local than previously thought, large numbers have recently been found in a few
new sites, but most of the 19th century sites have not been re-surveyed.