Borikhamxai Province occupies an area of 14,863 square kilometres and has a total population of 225,167 people (2005 census). It comprises six districts - Muang Borikham, Muang Thaphrabat, Muang Paksan, Muang Viengthong, Muang Pakkadeng and Muang Khamkeut. The capital is Muang Paksan. Borikhamxai Province contains part of the wilderness area known as the Nakai-Nam Theun National Biodiversity Conservation Area, the largest conservation area in the country at 3,700 square kilometres. In addition to the majority Lao population, Austro-Thai speakers are represented here by Lu, Lao Isaan and Lao Ngaew (Tai-Kadai/Tay-Thai/South Western Tay-Thai/Lao-Lu), Phuan, Tai Daeng and Tai Gapong (Tai-Kadai/Tay-Thai/South Western Tay-Thai/Tai), Seak, Tai Air, Tai Chiangki, Tai E, Tai Guan, Tai Khang, Tai Mene, Tai Meuy, Tai Oh, Tai Pao, Tai Pouark, Tai Pun, Tai Senkap, Tai Then, Tai Yor and Tai Yuang (Tai-Kadai/Tay-Thai/Northern Tay-Thai) and Hmong (Hmong-Mien); and Austro-Asiatic speakers by Kaleung (Mon-Khmer/Katuic), Khmu (Khmuic) and Bo, Krih, Liha, Phong, Phon Sung, Thavung and Tum (Viet-Muong). The area is also home to over a dozen threatened animal species, including Asiatic black bear, clouded leopard, elephant, giant muntjac, guar, Malayan sun bear and tiger. The sao la (spindlehorn) or vu quang ox - pseudoryx nghetinhensis – was discovered in neighbouring Việt Nam in 1992 and has been sighted several times since then in the Nakai-Nam Theun National Biodiversity Conservation Area. Only two other land mammals have been classified with their own genus this century. The first live sao la was captured in neighbouring Khammouane Province in 1996.