The important site in this area are swamps in estuary of Batang Toru River (also known as Rawa Lumut), with total area around 55000 ha, Rawa Batang Gadis (32000 ha), also including Siais Lake in opened swamp, and swamp around Natal (39000 ha) in the northern part.
This area is selected as important bird area because of the existence of White-winged Duck Cairina scutulata that recorded for the first time in northwest Sumatra in 1990 (Holmes 1990). Survey by Wibowo et.al. (1999) in Rawa Lumut found this bird, and it is estimated at least 5 birds of White-winged Duck present. Survey on the other locations in this area i.e.Danobirong Lake, Rawa Batang Gadis and Siais Lake couldn't find White-winged Duck Cairina scutulata (Wibowo et.al. 1999). Survey in Pandan Lake found 2-3 White-winged Duck (Hasudungan & Wibowo 2000)
Non-bird biodiversity: Other biodiversity include Prebytis cristata, Presbytis melanolophos, Hylobathes syndactilus, and Pongo pygmaeus (reported by local communities) (Giesen & van Balen 1992, Wibowo et.al. 1999).
BirdLife International (2020) Important Bird Areas factsheet: Rawa Pesisir Pantai Barat Tapanuli Selatan (Angkola). Downloaded from http://www.birdlife.org on 25/02/2020.