The large waterbird colonies of the Tonle Sap Great Lake, discovered in the mid-1990s, are of global importance. The colonies include the largest, and in some cases the only, breeding populations in South-East Asia of seven species of conservation significance, including two Globally Threatened species - Spot-billed Pelican (Pelecanus philippensis) and Milky Stork (Mycteria cinerea). It is also the largest remaining site for five Globally Threatened or Near-threatened species- Oriental Darter (Anhinga melanogaster), Lesser Adjutant Leptoptilus javanicus, Greater Adjutant (Leptoptilus dubius), Black-headed Ibis (Threskiornis melanocephalus) and Painted Stork (Mycteria leucocephala).
The Northern Plains of Cambodia support probably the largest breeding global population of Giant Ibis, a species known from only a handful of records in the 1900s until it was rediscovered in 2000. Until recently, the only known nesting sites in mainland Asia of White-shouldered Ibis (P. davisoni) were also located in the Northern Plains.
These two ibises are amongst the most threatened bird species in the world. In addition, the Northern Plains supports breeding populations of nine species of large waterbirds: Greater and Lesser Adjutants, White-winged Duck (CairiniaAsacornisscutulata) , Masked Finfoot (Heliopais personatus), Sarus Crane (Grus antigone), Oriental Darter, Black-necked Stork (Ephippiorhynchus asiaticus) and Woolly-necked Stork (Ciconia episcopus).