Key Biodiversity Khao Soi Dao Wildlife Sanctuary is the only IBA in Thailand known to supports the globally endangered Chestnut-headed Partridge Arborophila cambodiana, a restricted-range species confined to the mountains of south-eastern Thailand, and the Cardamom and Elephant mountains of south-western Cambodia. Chestnut-headed Partridge is one of two restricted-range species confined to the Thailand-Cambodia Mountains Endemic Bird Area; the second species, Cambodian Laughingthrush Garrulax ferrarius, is not thought to occur in Thailand. Khao Soi Dao Wildlife Sanctuary is also a wintering site for Silver Oriole Oriolus mellianus. In addition, the site supports three globally near-threatened species: Siamese Fireback Lophura diardi, Great Hornbill Buceros bicornis and Moustached Hawk Cuckoo Hierococcyx vagans. All of the species that occur in Thailand only in the south-east of the country have been confirmed to occur at the site, apart from Bar-bellied Pitta Pitta elliotti, which is only known from an unconfirmed record. The site is also of national conservation importance for a number of species characteristic of hill and montane evergreen forest, including Blue-rumped Pitta P. soror, Mountain Fulvetta Alcippe peracensis, Green Cochoa Cochoa viridis, White-tailed Robin Cinclidium leucurum, Lesser Shortwing Brachypteryx leucophrys and the southern Indochinese endemic race of Silver Pheasant Lophura nycthemera lewisi. The site qualifies under criterion A3 because it supports 17 species restricted to the Sino-Himalayan Subtropical Forests (Biome 08) and 18 species restricted to the Indochinese Tropical Moist Forests (Biome 09).