Nycticebus menagensis, Trouessart, 1897

Russell A. Mittermeier, Anthony B. Rylands & Don E. Wilson, 2013, Lorisidae, Handbook of the Mammals of the World – Volume 3 Primates, Barcelona: Lynx Edicions, pp. 210-220 : 219-220

11.

Bornean Slow Loris

Nycticebus menagensis

French: Loris de Menage / German: Borneo-Plumplori / Spanish: Loris perezoso de Borneo

Other common names: Philippine Slow Loris

Taxonomy. Nycticebus menagensis Trouessart, 1897 ,

Philippines, Tawitawi.

Extremely variable in color and size on the island of Borneo and surrounding small islands. Earlier authors recognized distinct taxa in the region. Two described by Lyon in 1906: bancanus, from Klabat Bay, Bangka Island, and borneanus from the Sakaiam River, Sanggau District, western Kalimantan, Borneo; and a third philippinus described by Cabrera in 1908, supposedly from Mindanao, but now restricted to the Sulu Archipelago, Philippines. In 1953, W. C. O. Hill subsumed these to subspecies of N. coucang . C. P. Groves in his taxonomic review of the genus published in 1971 concluded that these three forms should be considered junior synonyms of N. coucang menagensis . This taxonomy he maintained in subsequent publications in 2001 and 2005, as well as in a paper written with I. Maryanto in 2008. Current assessments based on museum specimens, however, suggest that these three forms may be taxonomically distinct. Their appearances are described below, but further research is needed. The form natunae described by Stone and Rehn in 1902, from Bunguran, one of the Natuna Islands,is considered by Groves to be a synonym of N. coucang , the Sunda Slow Loris, but modern-day photos ally it, in appearance, to the Bornean Slow Loris. Hill described it as russet in color with very dark facial markings and dorsal stripe, which does not match photos of slow lorises sent from Bunguran. This too deserves further investigation. Monotypic.

Distribution. Borneo, the islands off the SE coast of Sumatra Bangka and Belitung, and the Philippines (Sulu Archipelago); old reports from Mindanao are erroneous.

Descriptive notes. Head-body 27-30 cm,tail vestigial; weight 265— 800 g. The Bornean Slow Loris is the smallest of the Indonesian slow lorises, although weights vary considerably. The very smallest weights are adults from museum records, whose skins and teeth confirm adult status. This suggests that these animals may indeed be a distinct smaller species. In “true” Bornean Slow Loris, the fur is pale golden to red; head markings are virtually lacking, but a dark dorsal stripe is almost always present. Ears are short and close to the head, almost giving the appearance of no ears at all. There is a consistent absence of a second upper incisor. Three variants of the Bornean Slow Loris exist and correspond with earlier descriptions (see Taxonomy section). The form philippinus from the Sulu Archipelago in the Philippines is similar to typical N. menagensis (the “true form”), but itis even paler and almost always lacks a dorsal stripe. The form borneanus from West Kalimantan is easily confused with the Sunda Slow Loris (N. coucang ), but it is larger and more woody brown, with much darker facial markings, a deep woody brown dorsal stripe, longer fur, and more prominent ears; two variants of this forms exist with unique facial patterns. The form bancanus from Bangka Island is ruby colored and has no frosting;its facial markings are similarly rufousin tint, and the spinal stripe is ill-defined.

Habitat. Primary, secondary, tropical, moist, montane, evergreen, peat swamp, submontane evergreen, coastal lowland, riparian, dry coastal, gallery, and deciduous forests.

Food and Feeding. One observation was made of the Bornean Slow Loris eating gum. Based onits cranio-dental morphology, it has been proposed that it is more insectivorous than its congeners.

Breeding. The Bornean Slow Loris has not yet been held in captivity, and little is known about its breeding. It gives birth to a single infant. Infants have been seen throughout the year in Sabah, Malaysian Borneo.

Activity patterns. The Bornean Slow Loris is nocturnal and arboreal. It is sympatric with tarsiers in many parts of its range, and it might move higher in the canopy than other slow lorises as a result. It goes to the ground, butit is mostly seen above 10 m high in the forest.

Movements, Home range and Social organization. Very little is known about the social organization of the Bornean Slow Loris. It is very reluctant to enter traps. A first attempt to study it at the Sabangau National Park, Central Kalimantan, yielded only twelve sightings in 75 days. The median distance of a loris from the transect line was about 13 m, and all individuals were seen at heights of 15-20 m in the trees. Lorises were encountered singly, in mother—offspring pairs, or in adult trios. Two trios were observed in fruiting trees: Calophyllum hose: ( Calophyllaceae ) and Syzygium cf. nigricans ( Myrtaceae ). Another survey at Wehea, East Kalimantan, yielded similar results, with only one loris encountered in more than 30 km (0-02 ind/km). It was seen in the canopy at 30 m. Other attempts to find the Bornean Slow Loris have proved equally futile. In 46,000 trap nights in Kinabalu National Park, Sabah, K. Wells and coworkers caught only one animal (three times). J]. W. Duckworth reported in 1997 that he was unable to record loris presence in Similajau National Park, Sarawak, Malaysian Borneo, after 77 hours of nocturnal walks. In her study in the Lower Kinabatangan Wildlife Sanctuary, Sabah, Malaysia, R. Munds found low densities of the Bornean Slow Loris. The primary study site there, the Danau Girang Field Centre, was a riparian secondary forest. Only three lorises (on average at 20 m in the canopy) were spotted during 35 night surveys. All were alone and traveling between two trees by lianas or vines. All lorises were sighted at least 100 m away from any of the major rivers that surrounded the Danau Girang Field Centre. One loris, spotted at 05:30 h, moved along a branch toward a 15 m high thicket of vines and leaves. The sighting may indicate that such thickets provide sleeping sites for Bornean Slow Lorises.

Status and Conservation. CITES Appendix I. Classified as Vulnerable on The IUCN Red List. The Bornean Slow Loris appears to be rare throughoutits range, with a 30% reduction in its population over that last 24 years. Extensive use in the pet trade and habitat loss are primary threats. Ethnographic survey records suggest local extinction on some islands of the Tawi-Tawi group (Philippines), although it is still likely found on some other small islands. It occurs in a number of protected areas: Tasek Merimbun Wildlife Sanctuary in Brunei; national parks of Berbak, Bukit Baka Buki Raya, Kayan Mentarang, and Sabangau in Indonesia; and national parks of Bako, Crocker Range, Gunung Mulu, and Kinabalu in Malaysia.

Bibliography. Chen Jinghua et al. (2006), Duckworth (1997), Fooden (1991a), Groves (1971, 1998, 2001), Groves & Maryanto (2008), Hill (1953d), Munds (2010), Munds et al. (2008), Nekaris & Munds (2010), Nekaris & Nijman (2007b), Nekaris, Blackham & Nijman (2008), Nekaris, Collins et al. (2010), Nekaris, Shepherd et al. (2010), Ravosa (1998), Su Bing et al. (1998), Timm & Birney (1992), Wells et al. (2004).

Figures

1. Calabar Angwantibo (Arctocebus calabarensis), 2. Golden Angwantibo (Arclocebus aureus), 3. West African Potto (Perodicticus potto), 4. Milne-Edwards’s Potto (Perodicticus edwardsi), 5. East African Potto (Perodicticus ibeanus)

Distribution. Borneo, the islands off the SE coast of Sumatra Bangka and Belitung, and the Philippines (Sulu Archipelago); old reports from Mindanao are erroneous.