The Javan slow loris is a critically endangered nocturnal primate found in West Java, where it lives in montane forest and patchy farmland. It is a small, large-eyed animal that moves slowly through the trees after dark and spends the day hidden in dense cover. For anyone exploring the island’s wildlife, it is one of the most threatened animals on Java, and its survival depends on forest, farmland and the trade that reaches into both.
Status of the Javan slow loris and the pressures it faces
The species is classed as Critically Endangered on the IUCN Red List, the highest of the threatened categories. The reasoning behind that listing centres on habitat loss: the amount of forest suitable for the species has shrunk so far that less than a fifth of the suitable habitat is thought to remain. A suspected decline of over 80 percent over the last 24 years has been estimated, driven by exploitation and shrinking habitat.
The species is protected under CITES, the international treaty that regulates trade in wild animals and plants. Trade pressure is the second major threat after habitat loss. Javan slow lorises are taken from the wild for sale, and the animals that reach the market often suffer badly, with high mortality among those confiscated.
Where the species has been found in West Java
The Javan slow loris occurs across the western and central parts of Java, and in West Java it has been found in several upland and mixed landscapes. Mount Gede Pangrango is one of the best-covered sites. A 2014 field count there covered 23 transects totalling about 93 kilometres, and it estimated an overall density of about 15.6 animals per square kilometre, with a 95 percent confidence range of about 9.7 to 25.2. Densities varied widely between transects, from zero to 52 animals per square kilometre.
Mount Halimun Salak is another key area. That figure describes the amount of potential habitat rather than the number of animals, so a reader should not treat it as a population count.
Mount Ciremai also holds the species. A 2010 estimate put the number at 10 to 15 individuals across seven sites in Ciremai National Park, which shows how small and scattered some populations are.
How to read the density figures
Density figures for the Javan slow loris look precise, but they are local estimates rather than a national count. A density depends on how many animals are seen or detected in a given area, and that number changes with the time of night, the speed of the walk and the type of cover. Lorises are hard to count because they are quiet, slow and hidden in foliage, so a low count can reflect a difficult site as much as a scarce animal.
The safest reading is comparative. Across several sites the species turns up in forest, young regenerating forest and farmland mosaics, and the density varies from place to place. No single figure describes the whole island, and the fair conclusion is that the species survives in a patchwork of habitats that are shrinking and changing.
The talun landscape and why farmland matters
The talun is a patchwork of young regenerating forest and plantation, found in non-protected areas of West Java. It is not primary forest, and it is not the closed secondary forest of a national park. Figures from a set of talun sites suggest that densities there can be higher than in primary forest, with a value of about 25.5 animals per square kilometre compared with about 4.3 in primary forest and about 15.3 in secondary forest. Those figures come from a small number of sites and should be treated with care, since no national population count backs them up.
The lesson for conservation is clear even with that caution. Mixed farmland and young forest can hold lorises, and the animals may depend on it more than planners assume. Protecting the talun, rather than only the national parks, is part of the solution for this species.
Rehabilitation and releases in the Gunung Sawal area
Confiscated and surrendered lorises are taken to a rehabilitation centre at the foot of Mount Salak in Ciapus, Bogor. Animals there spend between six months and a year in care before they are ready for release. Before the final move, they spend two to four weeks in a habituation enclosure at the release site, where their behaviour is watched closely.
The Gunung Sawal Wildlife Reserve in Ciamis, and the Masigit-Kareumbi Conservation Forest nearby, have received releases in several rounds. In August 2018, twenty animals were moved to Masigit-Kareumbi and held in habituation, and a later batch of thirty-one was readied for release to Gunung Sawal and Masigit-Kareumbi. Twenty-five lorises had been released in the Mount Sawal reserve since 2014.
Post-release monitoring shows that the animals need time to settle. Work at Gunung Sawal fitted rehabilitated animals with radio transmitters and tracked their daily movements and home ranges over six months, from May to October 2018. Vertical space use shows that two months after release the animals spent much of their time in the canopy centre, while by four months they had moved into the 5 to 20 metre forest layer. Two to four months is not yet enough for a full return to natural behaviour, and loris bridges through the talun are recommended.
Translocation between sites also happens. Two females released earlier in the Halimun Salak forest were moved to Sawal because they had travelled close to the houses of a nearby village, which shows that release sites must be chosen with the animals’ movements in mind.
Javan slow loris and the trade in Jakarta markets
Jakarta is one of the main points where the trade is visible. In a 2012 count, observers saw 55 slow lorises for sale in two Jakarta markets, and three of them were Javan slow lorises. Traders kept selling despite the risk, and by 2017 dealers had moved part of the trade online, using social media and forums to avoid the markets.
Welfare is part of the problem. Traders clip the teeth of slow lorises so that the animals cannot bite the buyer or themselves. Confiscated animals often arrive in poor condition, and mortality is high in the period after rescue. Seizures have also included other primates, such as Javan langurs, which shows that the trade takes in several species at once.
How the Javan slow loris differs from the Javan gibbon and other primates
The Javan slow loris is easy to confuse with other island primates only at a glance. It is nocturnal, slow-moving and has very large eyes, and it has no tail. Its hands and feet grip branches firmly, and it spends the night feeding and moving through the canopy. The Javan gibbon, by contrast, is a diurnal ape that lives in pairs and is known for its loud solo songs at dawn. A visitor who hears a gibbon calling is not hearing a loris.
The Javan gibbon guide covers that ape in detail, and it is the best comparison for anyone who wants to tell the two apart. The loris also shares the island with the Javan leopard, which is one of the largest predators left on Java and is covered in its own guide.
Questions people ask about the Javan slow loris
Is the Javan slow loris the same as the Sunda slow loris? No. The Javan species is confined to Java, while the Sunda slow loris lives in a wider region of Southeast Asia. Both are nocturnal lorises, but they are different animals.
Where can it be seen in the wild? Visits to the species’ forest and farmland habitat are best left to experienced guides and field teams, since the animal is shy, nocturnal and easily disturbed.
What is the greatest threat? Habitat loss is the main long-term threat, and the pet trade is a serious and immediate one. Both are linked to the same farmland and forest edges where people live.
Can the species recover? Recovery depends on protecting forest and talun habitat, reducing trade and giving rehabilitated animals enough time to settle after release. Those steps are slow, and the outcome is not yet clear.
Next steps for a reader
A reader who wants the broader picture should begin with the Indonesian wildlife guide, which places the Javan slow loris among the animals of the archipelago. From there, the Javan leopard guide covers the island’s largest remaining predator, and the Javan tree frog guide shows another island species that depends on forest and farmland mosaics.
Related guides: blue-black kingfisher, Moon Orchid in Indonesia, flores giant rat, javan green magpie, Primates of Indonesia: Lorises, Monkeys, Gibbons and Orangutans.