The Pygathrix nemaeus is one of the three species of douc langurs, all of which are endemic to Indochina. Distinguished by its striking appearance, the endangered red-shanked douc langur can be spotted on trees in the forests of Lao PDR, and Viet Nam. Bach Ma National Park, an ASEAN Heritage Park In the northern part of Viet Nam is one of the protected areas where these arboreal species can be found.
Source: https://wwf.panda.org/discover/our_focus/wildlife_practice/profiles/mammals/douc_langur/