The cao vit gibbon Nomascus nasutus, also known as eastern black crested gibbon, is categorized as Critically Endangered on the IUCN Red List and was considered one of the world's 25 most threatened primates. The only known population occurs along the border between China and Viet Nam. Accurate information on population size and dynamics is critical for the species’ conservation, but population surveys conducted in only one country may over- or underestimate total population size because the home ranges of cao vit gibbon groups often cross the international border. In 2007 and 2016 we conducted two collaborative transboundary censuses of the cao vit gibbon populations in the Trung Khanh Cao Vit Gibbon Species and Habitat Conservation Area in Viet Nam and the Bangliang Gibbon National Nature Reserve in China. The results showed a population size of 102–110 in 2007, which increased to 107–136 in 2016. Our results indicate that previous surveys conducted separately in Viet Nam and China underestimated the global population size of this species. According to our more comprehensive surveys, the gibbon population is increasing slowly. The gibbons and their habitat are legally protected in both countries. Hunting and charcoal making have not been reported in this area since 2007. As habitat carrying capacity is a limiting factor, habitat restoration is required. However, lack of funding to protect the cao vit gibbon remains a challenge.

We conducted an interview survey around and within Mengla and Shangyong Nature Reserves, Mengla County, Yunnan, China, in December 2008 to ascertain whether gibbons were present in the area, and in December 2011 we surveyed two sites in the Reserves for the northern white-cheeked gibbon Nomascus leucogenys. We found no signs of the existence of gibbons during the survey. Illegal hunting was common at both sites. Only 36 individuals in nine groups were recorded in Mengla and Shangyong Nature Reserves in the 1980s, and this small and fragmented population was probably unable to survive the pressure of hunting. No white-cheeked gibbon was recorded in Huanglianshan Nature Reserve in a survey carried out by other researchers in 2003. Gibbons have a very low chance of survival in unprotected forest, and we conclude that the white-cheeked gibbon is extinct, or at least ecologically extinct, in China.

We conducted an intensive survey of the Vulnerable eastern hoolock gibbon Hoolock leuconedys along the west bank of the Salween River in southern China, covering all known hoolock gibbon populations in China. We found 40–43 groups, with a mean group size of 3.9, and five solitary individuals. We estimated the total population to be < 200. In the nine groups for which we recorded composition, seven comprised one adult pair and 0–3 offspring and the other two groups both comprised one adult male and two adult females. The population is severely fragmented, in 17 locations, with the largest subpopulation containing only five family groups. Compared with the population in 1985 and 1994 five subpopulations have declined and gibbons have been extirpated from nine localities, although we discovered two previously unknown subpopulations. Commercial logging, illegal hunting, agricultural encroachment and population fragmentation pose serious threats to the future of H. leuconedys in China. An integrated conservation plan, including nature reserve establishment/expansion, enforcement of existing laws, conservation education, translocation and conservation-oriented research are needed to ensure the survival of H. leuconedys in China.

The Critically Endangered black crested gibbon Nomascus concolor of China, Laos and Vietnam is threatened by deforestation and habitat destruction but there have been no studies of how it uses its forest habitat, probably because of the typically rugged topography and the species' shyness of humans. We studied the forest use of one habituated group between March 2005 and April 2006 on the border of Wuliangshan Nature Reserve, Wuliang Mountain, Yunnan, southern China. The group spent most of its time in the primary forest but preferred secondary forest in February when Leucosceptrum canum blossomed. They used dwarf forest occasionally but never used Eupatorium adenophorum grassland. Primary forest provided sleeping and singing trees, most food resources, safe cover and suitable locomotion supports. This forest is crucial for their survival but regenerates slowly. Even though secondary forest in the area has been regenerating for >50 years it provides only limited food resources for the gibbons. It may, however, comprise a good corridor for their dispersal. Dwarf forest provides a potential corridor for the group to disperse to a population on the other side of the mountain. Selective logging and agriculture encroachment should be forbidden in the primary forest on Wuliang Mountain. We recommend Alnus nepalensis, Myrica esculenta, L. canum and Betula alnoides as the pioneer species to recover the E. adenophorum grassland and for dispersal corridors.