The island of Borneo, located in southeast Asia at the southern edge of the South China Sea, is home to one endemic bird family, three endemic bird genera and 61 endemic bird species. All but one of the latter are forest dwellers, with most restricted to the spine of hills and mountains running down the middle of the island. The avian endemism has been shaped by the island's geological history. Borneo sits on a continental shelf. During glacial periods, when water levels were lower, Borneo was linked with other islands on the shelf and with the Malay Peninsula in a large landmass known as Sundaland. This allowed bird species to move freely throughout the region until the waters rose again as the glaciers melted. Separated from their relatives by the sea, some of these species evolved over millennia into the endemics now found on the island. BirdLife International has designated the mountainous central spine of the island as an Endemic Bird Area (EBA) because of the number of endemic species found there, and has further designated several lowland regions and nearby islands as secondary EBAs. Habitat destruction is a major threat to Borneo's endemic birds, as forests are lost to palm oil plantations and timber harvesting.