Category I: species that have been recorded in an apparently wild state in HK.
Category IIA: southeast China breeding species, the currently established HK breeding population of which is considered to derive from captive stock, but which probably occurred in HK prior to habitat changes.
Category IIB: extralimital species that, although originally introduced to HK by man, maintain a regular feral breeding stock without necessary recourse to further introduction.
Category IIC: previously established feral species.
Category III: species for which all published HK records are considered likely to relate to birds that have escaped or have been released from captivity.
*Category III species do not form part of the official HK List which is only Category I and II species.