The island of Java is heavily populated (density of >1000 people/km 2) and natural forest is found only scattered on many of the higher mountains. Forest loss reached its peak between 1850 and 1900, and although conversion and degradation have steadily reduced the available forest further, the pattern of forest fragmentation has remained fairly stable since (Koorders 1912; Whitten et al. 1996). As such, forest-dependent species, including the endemic Javan gibbon (Hylobates moloch), have been confined to isolated forest fragments for longer periods than many tropical species (Smith et al. 2017). This pattern of long-term fragmentation and isolation; the presence of relatively large (>500 individuals), intermediate (50-500 individuals), and small (<50 individuals) populations; and their extreme dependence on closed-canopy forest make the Javan gibbon a good model to study the population (conservation) genetics of tropical forest-dwelling species in a changing landscape. Kheng et al. (2018) recently presented data on the phylogeography and population genetic structure of Javan gibbons, collating data from three different studies; one from the late 1990s and two from the early 2000s, with a total of 47 gibbons. They group the samples into six areas: Ujung Kulon (UK, area inhabited by gibbons ca. 85 km 2), Mt. Halimun (HLM, ca. 270 km 2), Mt. Salak (SLK, ca. 70 km 2), Mt. Gede-Pangrango (GP, ca. 80 km 2), Mts. Masigit-Simpang-Tilu