Horton Plains Slender Loris / Ceylon Mountain Slender Loris Loris tardigradus nycticeboides Hill, 1942 Sri Lanka (2004, 2006)

Slender lorises are small, nocturnal primates occurring in southern India and Sri Lanka. The two recognized species, comprised of six subspecies, are readily distinguished from all other primate taxa by large, close-set eyes, pencil-thin limbs, and a long body with only a hint of a tail. Unable to leap, these ninjas of the night move with a fluid and noiseless locomotion. Though they may be slow when startled, all of the slender lorises studied so far can move several kilometers per night, and have home ranges of 1.5 to 10 ha—not small, considering that the various subspecies range in size from 110–350 g. The smaller of the two species, Loris tardigradus (Linnaeus, 1758), is found only in Sri Lanka’s diminishing rainforests. In the 1960s, W. C. Osman Hill used the loris as the symbol of the Wildlife and Nature Protection Society of Sri Lanka, stating that it, being the most mysterious and rarely seen creature of Sri Lanka’s jungles, was the most apt symbol for a society dedicated to revealing the unknown in nature. Two subspecies of this taxon, L. t. tardigradus and L. t. nycticeboides, are little better known today. The first long-term study of the red slender loris, L. t. tardigradus, was recently completed by Lilia Bernede of Oxford Brookes University, Oxford, UK. Continuing surveys of this subspecies by Nekaris and field assistants from the University of Ruhuna reveal that it is highly threatened, clinging to Sri Lanka’s small remaining rain forest patches, which average only 1,300 ha in size. The situation for the latter subspecies, L. t. nycticeboides, is no brighter. This rare little loris is found only in Sri Lanka’s chilly highlands (where temperatures may drop to -4°C). To cope with these extremes, the Horton Plains slender loris has evolved a thick, woolly coat, which swathes its limbs, giving it the superficial appearance of its Southeast Asian counterpart, the greater slow loris, Nycticebus coucang. Even in 1942, Osman Hill wrote “That the animal is rare in the Horton Plains is evidenced by the fact that Mr. Tunein-Nolthenius has been on the look out for it for the previous twenty years without success.” In 1980, this statement was further qualified by W. W. Phillips who stated that it “would appear to be the rarest of all mammals in Sri Lanka.” This mysterious loris first appeared on this list of the World’s 25 Most Endangered Primates in 2004, after Nekaris and Perera had carried out surveys for it at its type locality, the Horton Plains. They found only two animals after 60 km of surveys. This yielded an abundance estimate of 0.08-0.16 animals/km. A return visit in 2004 by Nekaris and colleagues from the Wildlife Heritage Trust yielded only one observation, giving an abundance estimate of 0.02 animals/km. These exceedingly low density estimates spurred Saman Gamage of the University of Ruhuna to lead a team in search of this most elusive of the lorises. Interestingly, after 21 nights of targeted efforts, abundance estimates generated in 2006 were the same: 0.02 animals/km. On the brighter side, Gamage’s team have found this loris in two new localities, Haggala Strict Natural Reserve, and Bomburella forest. An unusual museum specimen uncovered in the Natural History Museum of Colombo examined by Colin Groves also suggests that the range of this species may extend as far as Sri Lanka’s Knuckles Range, expanding its known area of extent from 30 km² to 250 km². A search to identify the lorises in this region will be instigated in 2007 by Sandun Perera of Sabaragamuwa University of Sri Lanka. Although still imperilled by continued habitat loss, gem mining, agricultural encroachment as well as being hunted and captured for medicines, as pets, and uses resulting from local folklore, there is a glimmer of hope for this small nocturnal primate. Virtually ignored since its discovery in the 1940s, media exposure from this list has now spurred two studies of this primate by local researchers. It is our hope that in 2008, more populations will be discovered, and that the Horton Plains slender loris can sink back into that dubious comfort of being ‘only Endangered.’ K. Anna I. Nekaris

References Bernede, L. In preparation. A Radio-Tracking Study of the Social and Behavioural Ecology of the Red Slender Loris (Loris tardigradus tardigradus) in Masmullah Proposed Forest Reserve, Sri Lanka. Phd Thesis, Oxford Brookes University, Oxford, UK. Hill, W. C. O. 1942. The slender loris of the Horton Plains, Ceylon. J. Bombay Nat. Hist. Soc. 43: 73–78. Nekaris, K. A. I. 2003. Rediscovery of the slender loris in Horton Plains National Park, Sri Lanka. Asian Primates 8(03):1–7. Nekaris, K. A. I. and J. Jayewardene. 2003. Pilot study and conservation status of the slender loris (Loris tardigradus and L. lydekkerianus) in Sri Lanka. Primate Conservation (19): 83–90. Nekaris, K. A. I. and J. Jayewardene. 2004. Survey of the slender loris (Primates, Lorisidae Gray, 1821: Loris tardigradus (Linnaeus, 1758) and Loris lydekkerianus Cabrera, 1908 in Sri Lanka. J. Zool., Lond. 262: 1–12. Nekaris, K. A. I., S. N. Gamage and B. V. P. Perera. 2007. Loris tardigradus nycticeboides. In: Guide to South Asian Primates for Teachers and Students of All Ages, S. Walker & S. Molur (eds.), p.18. Zoo Outreach Organisation, PSG South Asia and WILD, Coimbatore, India. Phillips, W. W. A. 1980. Manual of the Mammals of Sri Lanka. 2nd ed. Wildlife and Nature Protection Society, Sri Lanka. Werner, W. L. 1984. Die Höhen- und Nebelwälder auf der Insel Ceylon (Sri Lanka). Tropische und subtropische Pflanzenwelt 46. Steiner, Wiesbaden. Suggested citation: Nekaris, K. A. I. 2007. Horton Plains Slender Loris, Ceylon Mountain Slender Loris, Loris tardigradus nycticeboides Hill, 1942. In: Primates in Peril: The World’s 25 Most Endangered Primates 2006–2008, R. A. Mittermeier et al. (compilers), pp.12-13. Unpublished report, IUCN/SSC Primate Specialist Group (PSG), International Primatological Society (IPS), and Conservation International (CI), Arlington, VA.