In March 2009 observations of Lao langurs were made on several days for many hours in the northern part of Phou Hin Boun National Biodiversity Conservation Area (NBCA). Single males and a group with 14 adult and subadult animals, and three yellow juveniles were observed. Currently there is no agreement about the systematic position of the taxon. Molecular genetic differences between Lao langur and Hatinh langur places the taxa on subspecies level. In April 2009 three black langurs were observed

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... in the southern part of Phou Hin Boun National Biodiversity Conservation Area. The taxonomic status of the black langur which occurs in northern central Vietnam and central Laos is still unclear. Molecular genetic studies of one individual kept at the EPRC correspond with the type specimen in Smithsonian Museum, and also with the Hatinh langur. It seems that these all-black individuals are a melanistic morph of the Hatinh langur. The white headed Laos langur and the black langur occur both in the southern part of Phou Hin Boun NBCA. Based on the current state of knowledge and information from the recent surveys, both forms are separated and should also use different habitats. The limestone range in Hin Nam No NBCA-with records of black langurs-has a spur towards the west until the Mahaxai limestone range, south of Phou Hin Boun NBCA. The large valley of the Bangfai river between the Mahaxai limestone range and Phou Hin Boun NBCA do not currently act as zoogeographical barriers, but the nature of this large valley and alluvial land indicate a possible historical separation between the northern Phou Hin Boun limestone range and the southern limestone range east of Mahaxai. A connection between the two taxa-the black morph of the Hatinh langur south of the Bangfai river, and the Lao langur north of the Bangfai river-likely exists only since recent palaeoglacial times. It would be interesting to study the possibility of different niches between the taxa and likelihood of interbreeding actions.