Terrestrial species from the Lao People’s Democratic Republic (PDR) are under high threat due to deforestation and overhunting. Previous studies have even defined these forests as subjected to an “empty forest syndrome”, a condition in which forests that are apparently well preserved are instead almost deprived of vertebrate faunas due to extreme exploitation by local communities. Forest specialists, including several primates, are among the most threatened species in the country. The Laotian langur (Trachypithecus laotum) is endemic to Lao PDR, is listed as Endangered by the IUCN Red List, and it is one of the least studied species in the region. A survey on the local distribution, life history and conservation status of the Laotian langur was carried out in Phou Hin Poun National Protected Area, Khammouane Province of Lao PDR. The survey consisted of an initial phase with interviews to select key informants on the Laotian langur and the other primate species of the area. Then, a phase of field surveys along forest transects, totaling 64.1 km of 21 transects, yielded a record of 35 individuals in 9 groups. The highest encounter/detection rate of the Laotian langur was 1 group per km at one sector of the park. In contrast, it was much lower (0.18–0.34 groups/km) in the rest of the protected area. The group sizes were much lower than those observed in the same area between 1994 and 2010, thus suggesting a decline in the population size of langurs. This decline may be linked to habitat loss (timber extraction and mining). Still, also overhunting, as signs of poaching were observed during our field surveys. This was also supported by the reports of our interviewees. Laotian langurs were observed to be sympatric and interact while foraging with the Assamese macaque (Macaca assamensis). In the cases of sympatric occurrence between the two species, we observed that subtle mechanisms of niche partitioning may occur to reduce interspecific competition for food. Further research on the population and ecology of this endangered langur should be conducted to understand the species and aid its conservation.

Monitoring the status of endangered wildlife is a critical foundation for biodiversity conservation efforts. The use of autonomous acoustic recorders to monitor wildlife has become increasingly popular in terrestrial tropical systems. However, these recorders are expensive and not available for purchase and repair in all countries. The development of easy‐to‐use and low‐cost devices is therefore needed for applications worldwide. In this study, we modified and installed smartphone devices to operate and record sounds produced by the Vietnamese Crested Argus Rheinardia ocellata in Kon Chu Rang Nature Reserve, Vietnam, in 2021. We used the software package RAVEN to create spectrograms and to identify Crested Argus calls from acoustic recordings and used the program MARK to estimate occupancy and detection probabilities. We recorded calls of Crested Argus at 16 of 40 locations and most calls were recorded in the northern and eastern parts of the nature reserve. Our model‐averaged estimates of detection probabilities indicated that detection in the morning or afternoon was c. 0.50 and constant over seven sampling days. Our overall average occurrence probability of Crested Argus was 0.43 (standard error = ±0.08), but we found occupancy to be positively correlated with distance to the nearest village, indicating that poaching may negatively affect this species. Based on these data we suggest that the Kon Chu Rang Nature Reserve and possibly two adjacent nature reserves, namely An Toan Nature Reserve and Ba To Proposed Nature Reserve, might be important sites for Crested Argus.