1508 species that have occurred in India, Bangladesh, Pakistan, Nepal, Bhutan, Maldives, the Chagos archipelago and Afghanistan are covered, including 85 hypothetical and 67 'possible' species, which are given only short accounts. Notable aspects of "Birds of South Asia" are its distribution evidence-base – the book's authors based their distributional information almost completely on museum specimens – and its taxonomic approach, involving a large number of species-level splits. Its geographical range was also greater than that of older works, notably in the inclusion of Afghanistan.