Improved protected area management, in particular improved law enforcement, in Popa Mountain Park and Panlaung-Pyadalin Cave Wildlife Sanctuary is essential to stabilize the two largest known populations. Mount Yathae Pyan is an isolated karst hill. This population could be protected through the designation of a community-protected area (CPA). The forests in Bago Yoma are severely degraded and fragmented, but could still provide the largest, contiguous habitat if deforestation and forest degradation are reversed through improved forest protection and restoration. The status of most populations is poorly understood, and additional surveys are urgently required. Furthermore, Trachypithecus popa needs to be added to the national and international lists of threatened species.
This species is found between the Ayeyarwaddy and Thanlwin rivers in the central dry zone of Myanmar and into the western foothills of the Kayah-Karen Mountains. The northeastern limit is undefined, but the species may occur throughout the Kayah-Karen Mountains. This species is endemic to Myanmar (Roos et al. 2020).
As evident from historical records (museum specimens and travel notes), the species was once widespread in the central dry zone of Myanmar. Only two of these subpopulations are known to have survived (Mount Popa, Bago Yoma), while all others are considered possibly extirpated. However, during recent fieldwork, three new subpopulations were discovered. At Myogyi Monastery, the langur population is estimated at 75–100 individuals (Quyet et al. 2019), but these langurs are probably hybrids between Trachypithecus popa and T. melamera (Roos et al., 2020). The subpopulations at Panlaung-Pyadalin Cave Wildlife Sanctuary, and Mount Yathae Pyan, consist of 46–96 individuals (Quyet et al. 2019) and 20–30 individuals (Aung Ko Lin and Aung Lin pers. obs.), respectively. The subpopulation at Bago Yoma contains about 22 individuals (Aung Ko Lin pers. obs.) and at Mount Popa, field surveys conducted in 2019 revealed a population size of 111 individuals (Thaung Win pers. comm.). Mount Popa was declared a national park (Popa Mountain Park) in 1989 and has an area of 128.54 km², including 26.97 km² classified as suitable to highly suitable for langurs (Thant 2013, Thant et al. 2013). According to Nang Wah Wah Min et al. (2006) average percentage of adult individuals is 68% per group at Mount Popa. The total population of Mount Popa was 196 individuals in 2005 (Nang Wah Wah Min et al. 2006). Surveys in 2019 resulted in a population size of only 111 individuals, resulting in a decrease of about 43% within 14 years in the largest known subpopulation. This subpopulation is also the best protected of all four subpopulations. For the three others, an even larger decline must therefore be assumed. Given these data, a population reduction of at least 90% over the last three generations (or 33 years) is suspected.
Throughout its range, Trachypithecus popa is threatened by hunting, habitat loss, degradation, and fragmentation caused by agricultural encroachment, illegal/unsustainable timber extraction, and disturbances caused by collection of non-timber products and free cattle grazing (Quyet et al. 2019, Thant et al. 2013). For example, between 2001 and 2019, Myanmar had an 8.6% decrease in tree cover (Global Forest Watch 2020).