The lower zones hold secure populations of the endangered West Javan gibbon (Hylobates moloch moloch) - a sub-species of the silvery gibbon. Mount Halimun is its most secure habitat, but its range is restricted to a thin ring around the park as the species is not found above 1,200 metres. Javan lutung (Trachypithecus auratus), and other endemic species are evident; about half its 145 known bird species are rarely seen elsewhere in Java.