Fame beckons at last for the Horton Plains slender loris


After I'd finished writing about the new Madagascan mongoose, I thought it only right to add material to the end of the article about some of the other new discoveries made in the world of mammalogy. But, as happens on so many occasions, this made the article over-long and in the end I decided to axe that additional stuff. Plus, it makes more sense to get two, three, four or more articles out of one - another familiar theme on Tet Zoo (errr, gekkotans, anurans, babirusas, matamatas, pronghorns, bird hands.... need I go on?). Anyway...


From Sri Lanka comes the news that the Horton Plains slender loris (also known as the Highland slender loris or Montane slender loris) has been photographed: it's only been observed in the wild four times since its discovery in 1937, and this is the first time it's been captured on camera [adjacent photo © by C. Mahanayakage; from Gamage et al. (2010)]. What hasn't been mentioned by the popular media is that a technical paper has been published on this event, and it discusses the significance of the new data that was collected (Gamage et al. 2010).

As happens whenever a species (or subspecies) is reportedly seen, or photographed, for the first time ever, or for the first time in a while, reports in the media are rather confused. Claims that the Horton Plains slender loris was "thought extinct for 65 years" haven't been true since 2002, because in that year it was rediscovered following its 'absence' since 1939 (Nekaris 2003). So, post-2002, primatologists knew that the animal was still around; they just regarded it as rare and very localised in distribution (its range is perhaps as small as 30 sq km). Primatologists had tried to find it prior to 2002, but such attempts were unsuccessful until loris researcher Anna Nekaris observed a single individual. Or, rather, the eye-shine of one (Nekaris 2003).


The new photos were taken by a team from the Zoological Society of London and their Sri Lankan colleagues. They were looking specifically for the loris. The ZSL researchers represent part of the EDGE programme: something I hope you're familiar with (EDGE = Evolutionary Distinct and Globally Endangered).

What is the Horton Plains slender loris anyway? It's actually a subspecies of the Red slender loris Loris tardigradus, named L. t. nycticeboides by W. C. Osman Hill in 1942. Hill (1942) described how two specimens were discovered in 1937, and this was after a lengthy search, showing that they were hard to find even then. These two individuals were taken into captivity, they bred (producing two offspring), and one of those offspring serves as the holotype [the painting below - from here - was produced when "No figures of live animals of this form seem to be available"].


Compared to other slender lorises (all of which inhabit India and Sri Lanka), the Horton Plains slender loris has proportionally shorter, stockier limbs and thicker, longer fur, and it thus superficially resembles a slow loris. Presumably, these are adaptations that help it to cope with the cool - and even very cold (below freezing) - temperatures that occur in its montane habitat. Wow - it's a cold-adapted strepsirrhine (strepsirrhines are lemurs and kin [Lemuriformes] and lorises and bushbabies [Lorisiformes]) [slender lorises of unspecified taxon shown below, from Richard Lydekker's Royal Natural History Volume 1].


The distinctive morphology and ecology of the Horton Plains slender loris mean that it's yet another of those highly distinctive 'subspecies' that might well warrant recognition as a distinct species. Loris taxonomy is a rather convoluted subject: there's debate about which names should be used for which forms, and there are also suggestions that several additional forms (both subspecies and species) should be named. Some authors have used the name Loris lydekkerianus for all slender lorises except the nominal L. t. tardigradus (Groves 1998), in which case the Horton Plains slender loris is L. l. nycticeboides. However, inclusion of nycticeboides in L. tardigradus now seems more favoured (Groves 2001). I'm going to have to resist the urge to discuss or even mention the other slender loris taxa, sorry. And don't get me started on slow lorises (Nycticebus).

Lorises are sometimes regarded as primate analogues of tree sloths - in fact, one name used on Sri Lanka for slender lorises is Ceylon sloth - and they've typically been characterised as 'stealthy' climbers. They don't leap, and some primate workers have proposed that this slow movement helps lorises remain cryptic and unnoticed by predators (e.g., Walker 1969). Their slow, quadrupedal, hand-over-hand arboreal locomotion could perhaps be regarded as sloth-like, except lorises climb above branches (rather than below them), use grasping hands and feet (rather than suspension via hooked claws), and are predators of insects and vertebrates (rather than folivores: in fact, lorises have been described as the most predatory of all primates. In some populations, animals make up 100% of the diet). So, not similar to sloths at all, really.

And slender lorises aren't really that slow anyway: for about a quarter of the time that they're moving, red slender lorises move rapidly (Nekaris & Stephens 2007) [at about 1.29 m/sec: that translates to 4.64 km/h or 2.89 mph. It doesn't sound fast (it's similar to normal human walking speed), but it is for an animal of this size, apparently]. One interesting question is whether this rapid arboreal locomotion is a retained primitive feature, or a specialisation of the slender loris lineage. By the way, slender lorises are another of those animals sometimes stated to be unable to swim (Nowak 1999).

A brief aside on the venomosity of the slow loris


I can't finish this article without mentioning the fact that glands on slow loris (note: NOT slender loris) arms secrete a toxin that becomes activated by saliva (the lorises lick the glands, thereby mixing the toxin with saliva in the mouth). People have sometimes gone into anaphylactic shock after receiving slow loris bites (Wilde 1972, Krane et al. 2003). The toxin seems to be an allergen. International trade in slow lorises was banned in 2007, but prior to this they were sold as pets (often with their canines filed down or removed).

Clearly, more information is needed on the conservation status of the Horton Plains slender loris, and it's likely that habitat fragmentation and degradation, and possibly climatic change, pose threats to its survival (Gamage et al. 2010). In part of southeast Asia (like Cambodia), lorises are used in traditional medicine (I think I recall reading that people eat their eyes for some stupid reason), but this seems not be a problem in Sri Lanka. Lorises have also suffered from exploitation by the pet trade, and lorises in India are often killed by electrocution from power lines. Ongoing research on the Horton Plains slender loris and other loris taxa is underway, and a better understanding of these bizarre, fascinating primates, and of their conservation priorities and the threats that face them, should result.

Primates haven't been much featured on Tet Zoo - they're just one other of those groups I've never gotten round to focusing on, yet - but do check out...

Refs - -

Gamage, S., Reardon, J. T., Padmalal, U. K. G. K., & Kotagama, S. W. (2010). First physical examination of the Horton Plains slender loris, Loris tardigradus nycticeboides, in 72 years Primate Conservation [Published electronically prior to print publication].

Groves C. P. 1998. Systematics of tarsiers and lorises. Primates 39, 13-27.

- . 2001. Primate Taxonomy. Smithsonian Institution Press (Washington, DC).

Hill. W. C. O. 1942. The slender loris of the Horton Plains, Ceylon, Loris tardigradus nycticeboides subsp. nov. Journal of the Bombay Natural History Society 43, 73-78.

Krane, S., Itagaki, Y., Nakanishi, K. & Weldon, P. 2003. "Venom" of the slow loris: sequence similarity of prosimian skin gland protein and Fel d 1 cat allergen. Naturwissenschaften 90, 60-62.

Nekaris, K. A. I. 2003. Rediscovery of the Ceylon Mountain Slender Loris in the Horton Plains National Park, Sri Lanka. Asian Primates 8 (3), 1-7.

- . & Stephens, N. J. 2007. All lorises are not slow: rapid arboreal locomotion in the newly recognised red slender loris (Loris tardigradus tardigradus) of southwestern Sri Lanka. American Journal of Primatology 69, 112-120.

Nowak, R. M. 1999. Walker's Mammals of the World, Sixth Edition. The Johns Hopkins University Press (Baltimore and London).

Walker, A. 1969. The locomotion of the lorises with special reference to the potto. East African Wildlife Journal 7, 1-5.

Wilde, H. 1972. Anaphylactic shock following bite by a 'Slow loris,' Nycticebus coucang. American Journal of Tropical Medicine and Hygiene 21, 592-594.


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Lorises are excellent creatures - so charismatic with those mournful eyes. I love seeing them in nocturnal houses but it always annoys me that our eyesight is so naff at low light levels. I am constantly frustrated by hearing Morepork (NZ Boobok owls) calling in my back garden and not being able to see them (or find them with a torch).

Anyway does the paper explain how they found them? I assume they used night vision goggles whilst active searching - or did they lure the Lorises into a feeding station somehow - or was it just waving torches about?

By RStretton (not verified) on 04 Aug 2010 #permalink

You need to have white light and keep it at eye level (like headtorch). And it is best not to switch the light on at owl, but point it to the side and slowly move. Eyes of owls shine much less than nighjars and most mammals. Don't know about loris, though.

Rich: the authors found the loris thus...

"Our methods involve teams of two field biologists systematically searching the forest habitat visible from the predetermined transect track. They walk at a slow
pace of about 1 km per hour, looking for eye shine with dimmed, wide-beam and heavily red-filtered head torches (LED lenser⢠H7)." (Gamage et al. 2010, p. 2 of preprint).

Brian: several fossil taxa seem to be fossil lorids, including Karanisia clarki from the Middle Eocene of Egypt, Nycticeboides simpsoni from the Miocene of Pakistan, Mioeuoticus bishopi from the Early Miocene of Uganda and M. shipmani from the Miocene of Kenya. There are other, unnamed bit and pieces too, plus there are fossil galagos going back to the Eocene. Indeed, Karanisia and the Eocene galagos show that the loris-galago divergence has occurred by the Eocene (Seiffert et al. 2003).

Ref - -

Seiffert, E. R., Simons, E. L. & Attia, Y. 2003. Fossil evidence for an ancient divergence of lorises and galagos. Nature 422, 421â424.

Presumably, these are adaptations that help it to cope with the cool - and even very cold (below freezing) - temperatures that occur in its montane habitat. Wow - it's a cold-adapted strepsirrhine

It is probably not unique in that regard though. Some African galago species live at comparable or even slightly higher altitudes and thus presumably have to deal with similar temperature conditions. (For example, the Uluguru bushbaby Galago orinus, which is a montane forest specialist, is found at altitudes of at least 2400 metres in Tanzania's Eastern Arc Mountains.)

lorises have been described as the most predatory of all primates

I'm nitpicking again, but surely tarsiers are non-herbivorous to an equal if not greater extent than lorises?

On coping with cold conditions - yeah, I didn't say that the Horton Plains slender loris is unique in this regard. Indeed some galagos are said to get frostbitten tails.

And, yes, tarsiers are 100% predatory too: I should have said that slender lorises "have been described as among the most predatory of all primates", my bad.


slow lorises sometimes kill tarsiers

That was news to me. Would you by any chance happen to know the original reference?

(I knew that orangutans, in turn, sometimes opportunistically kill and eat slow lorises. That would make orangutans primates that prey on primates that prey on primates.)

And what that make of Dayak hunters? ;)

I think an analoge with tongueless Chameleons is probably more appropriate.
Though I didn't know Lories were that fast.

By Wilbert Friesen (not verified) on 06 Aug 2010 #permalink

The comment about them being unable to swim is probably not accurate. According to what I recall of a lecture I went to here at Bristol, a rehabilitation centre made the mistake of keeping lorises in a moated enclosure. Unfortunately, it was also opposite an aviary..

It was then they discovered how predatory they are as well.

Incidentally, the pigmy slow loris at least in the north of its range appears to be a semi-hibernator. In the autumn they put on a lot of weight and become very inactive during the winter months when insect prey is scarce.

Holy balls, the slow loris is my favorite animal in the universe! Well, favorite mammal anyhow. So cute! It is maybe their biggest curse, as many are nabbed for the pet trade. I wanna kill all the mofos on youtube with pet lorises, with mind bullets.

THEY EAT TARSIERS??? That's new on me. That's new on the zookeepers at Woodland Park Zoo in Seattle as well, because they had them in the same enclosure for a while. Ha!


By CS Shelton (not verified) on 07 Aug 2010 #permalink

@ 8, @ 12,

the original reference can be found in Kurt Kolar's chapter on the Tarsier in the Grzimek Enzyklopädie Säugetiere; Kolar mainly relies on Niemitz as his primary source. Note that Niemitz watched the loris stalking the tarsier, but intervened before it could kill (and eat?) the smaller primate - clearly a violation of the prime directive ;-).

Clearly. :-)

By CS Shelton (not verified) on 09 Aug 2010 #permalink