The IOC Oriental Region checklist is a subset of species from the complete IOC world list. This provides an alternative to the Oriental Bird Club (OBC) list, which covers a slightly different geographical region with a less up to date taxonomy.
The Oriental Region comprises most of the Indian subcontinent, all of southeast Asia, Indonesia (except for West Papua and nearby islands), the Philippines, Taiwan and southern parts of China including Hong Kong. Areas further north in Asia (northern and central China, Tibet, Mongolia, Japan, North and South Korea, Russia and Central Asia) are excluded: they fall within the Palearctic region.
In China, provinces from Yunnan eastwards, north to approximately Shanghai, are Oriental, whereas areas further north such as Beijing and Beidaihe, Qinghai and the mountains of Sichuan fall in the Palearctic. Further details of the boundary in China can be found in the British Birds paper "The boundaries of the Palearctic region".
In southeast Indonesia, the islands of Wallacea (Sulawesi, Halmahera, the Lesser Sundas, the Moluccas) are a transitional zone between the Oriental and Australasian regions. Lydekker's Line has been used as the eastern boundary for this list, thus all of Wallacea is included.
The western boundary in Pakistan follows the Indus river. Purists may wish to exclude very high altitude areas in Nepal, Bhutan and the very north of India, where the species composition is more closely aligned with the Palearctic.