东黑冠长臂猿是极度濒危物种，全球种群数量极其稀少。2015年5月和8月，采用在固定地点监听鸣叫的方法在广西邦亮长臂猿国家级自然保护区内对东黑冠长臂猿开展两次实地调查，发现在中国境内形成了由1只成年雄性，2只成年雌性和1只婴猿组成的新群体。这是自2006年该物种在中国被重新发现后，首次在中国境内发现形成新群体。中国境内东黑冠长臂猿的种群数量也由3群22只，增长到4群26只。有限的栖息地可能是未来限制东黑冠长臂猿新群体形成的主要因素之一，所以栖息地恢复对东黑冠长臂猿种群数量增长尤为重要。放牧不利于栖息地恢复，要逐步减少，进而杜绝在保护区内放牧。另外，东黑冠长臂猿跨国界分布，中越两国政府之间应加强协调，避免在保护区内实施对栖息地不利的边境管理活动。如果两国间出现种群隔离，对东黑冠长臂猿种群数量的增长将会非常不利。

Eastern black crested gibbons (Nomascus nasutus) are listed as Critically Endangered in the IUCN Red List, because of their small population size. The single remaining population is comprised of about 110 individuals living in a karst forest patch along the border of China and Vietnam. We monitored gibbon calls from fixed listening posts to survey the Chinese population in Guangxi Bangliang National Nature Reserve (Bangliang NNR) during May and August of 2015. We found a previously unknown group of eastern black crested gibbons that consists of 1 adult male, 2 adult females, and 1 infant. This is the first discovery of a newly formed group in China since 2006, when the species was rediscovered in Bangliang NNR. The population of eastern black crested gibbons in China is now estimated to have increased from 22 individuals in 3 groups to 26 individuals in 4 groups. The population size is likely limited by available habitat, restoration of which will be vital to future population growth. Presently, livestock grazing is a serious threat to gibbon habitat in Bangliang NNR. Actions must be taken to reduce or even prohibit grazing inside the nature reserve. Given that this population is distributed across the border of China and Vietnam, relevant government departments in both countries need to strengthen cooperation in border management and habitat protection. Fragmentation of this population by the international border would harm its recovery.