The species is widely distributed west from the Indian subcontinent (but not in Sri Lanka despite an old report of a skin of doubtful provenance) extending east across Southeast Asia. Slight differences in size and plumage are noted in different parts of their range and several subspecies have been designated. The nominate form is found from India to Thailand. Subspecies lignator described by Swinhoe in 1861 is larger and found in southeastern China and Taiwan. Subspecies javanensis described by Dumont in 1818 is smaller and found across the larger islands along the Malay Peninsula extending east to the Philippines. Some island forms are larger and these include sarasinorum described by Stresemann in 1912 and found on Sulawesi, the Sula Islands, Lesser Sundas and Timor. The form on the Moluccas, medius described by Bonaparte in 1850, is the largest. Some other subspecies like philppinensis from the Philippines and chamnongi from Thailand are not always recognized and are thought to form either variants or intermediate plumages. The population patchily distributed in the Western Ghats of southern India may constitute a distinct subspecies.