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Population viability analysis is a predictive procedure that uses a combination of different modelling approaches to estimate species vulnerability to extinction. Javan gibbons ( Hylobates moloch ) are vulnerable to local extinction primarily due to loss of habitat and hunting for the illegal pet trade. Using the modelling software VORTEX, we assessed the status of Javan gibbons in 3 areas (Ujung Kulon National Park, Halimun-Salak National Park, and Dieng Mountains) which hold over half of the remaining estimated number of gibbons on Java. Ujung Kulon and Halimun-Salak are long-time protected areas, whereas Dieng Mountains remain unprotected. For each area, we calculated the probability of extinction over a 100-year time period by testing different area-specific scenarios (e.g., hunting, deforestation, and increase in carrying capacity). Our modelling suggests each of the populations has …