Several subspecies have been proposed for the plumage and size variation seen in different geographic populations. The nominate form is from China (Canton), which is also the origin of the introduced population in Hawaii. Subspecies formosa from Taiwan has been considered as doubtful and indistinguishable from the nominate population. The population in India suratensis (type locality Surat) and ceylonensis from Sri Lanka have fine rufous or buff spots on the back. There is a size reduction trend with specimens from southern India being smaller, and ceylonensis may merely be a part of this cline. The lesser and median wing-coverts are also spotted at the tip in buff. This spotting is lacking on populations further north and east of India, such as tigrina, which also differ greatly in vocalizations from the Indian forms. The population from Hainan Island is placed in hainana. Others like vacillans (=chinensis) and forresti (= tigrina) and edwardi (from Chabua = suratensis) have been considered invalid.
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