Slender in the night: long unstudied, the slender loris of South Asia emerges from primatology's shadows

by K.A.I. Nekaris

What is a slender loris? Given the name, one could hardly be blamed for thinking it's something out of a Dr. Seuss book. And a quick glance at the animal's lithe body and pencil-thin arms might suggest it's a rat or a squirrel (and might immediately indicate why it is sometimes called "a banana on stilts"). Closer examination, however, reveals the loris's close-set eyes and the nails on its feet and hands. A look inside its skull reveals a large brain. Indeed, this animal is neither a mutant plantain nor a rodent. It is a primate, close kin to the bushbabies of sub-Saharan Africa and the lemurs of Madagascar.

These facts about the loris, a native of southern India and Sri Lanka, have been known for some time. But despite being the subject of numerous now-obscure nineteenth-century reports, this small, nocturnal, gremlin-like prosimian long went unexamined by primatologists. Only in recent decades have prosimians--a suborder of primates that includes lemurs, lorises, bushbabies, and tarsiers--begun to be studied systematically. The earliest of these modern investigations emphasized the various species' physical and social similarities and sought, on the basis of these similarities, to reconstruct the behavior of the first primates--also nocturnal, also generally small animals, which evolved about 50 million years ago. More recent studies, however, have uncovered unexpected diversity among extant prosimians, and the group's once-simple portrait is now being redrawn.

Since 1996 I have been traveling to southern India and Sri Lanka in search of the elusive slender loris. Initially I looked for these animals in the forests of India, where I'd hoped to arrive at an estimate of how many remained in the wild, for even such basic information had not yet been recorded. But before I could count lorises I had to find them, and for the first three months I caught fleeting glimpses of retreating lorises on only fourteen occasions. I had little hope of ever seeing them close-up in the wild.

I got my break when an Indian colleague came across an old fortune-teller and his furry "familiar"--a loris whose job it was to pick cards out or a deck with his eerily long arms. When questioned, the old man very hesitantly revealed the name of the forest where he had obtained his companion. Several of my colleagues (associated with the Indo-US Primate Project) set out immediately for the place, a dry, deciduous forest nestled in the foothills of the Eastern Ghats. Once there, they saw more lorises in one night than we had during three months of carefully searching all the major national wildlife refuges in southern India.

I returned to India in the autumn of 1997 to begin a long-term study of the slender loris. Given my experiences the previous year, I would have felt gratified to find one of them within a week. To my delight, I saw more than sixty animals within a few hours during a drive my first night in the area. Lorises were everywhere: crossing the road, walking along thorny fences, climbing banana plants, even sitting on tea shop roofs. It seemed that all the lorises in India had moved to one small corner of the Eastern Ghats.

My first task was to search for a study site where I could work for the next year. I wanted one with short trees, high visibility, and lots of lorises--and I found such a site almost immediately. Houses, cropland, noisy villagers, and even noisier cinema loudspeakers surrounded it. Accustomed to this racket, the animals proved to be intrepid, and I was able to follow them closely, usually from within five feet. From that distance I could identify individuals by the tiniest of features--missing toes, scraggly fur, heart-shaped noses--and see the most minute details of behavior, right down to which little insect they were gobbling up.

This study site became the crucial factor in freeing the loris from being thought of as a "living fossil." Not just a creature that shed light on the earliest primates, it was a real animal roaming the forests of South Asia. Because of the darkness, the dense woods, and the primates' small size and fast moves, studies of nocturnal prosimians often are possible only with the use of radio tracking, night-vision equipment, and elaborate trapping schemes. Making observations as extensive as those recorded for diurnal primates--monkeys, apes, and some lemurs--is often quite difficult, but thanks to the easy visibility at my study site, I could follow the animals for twelve hours at a stretch.

Most nocturnal primates have been reported to lead relatively solitary lives, rarely coming into physical contact with others (except for mating and the nursing of young). Some species use scent markings to communicate; others employ a wide variety of trills, "kriks" and whistles. For the most part, these generally solitary primates are gregarious only at communal sleeping sites, where they huddle, groom, and carry on other activities common throughout the primate order.

No one had expected slender lorises to be different, but I found they clearly were. My first sightings involved multiple animals--up to five in a single bush. Pairs were even more common, and many of their get-togethers, which lasted up to several hours, did not occur at sleeping sites. During these meetings the lorises groomed one another, play-wrestled, and fed. As my study continued, I realized that these activities reflected the species' numerous and complex social connections (a later study I did in Sri Lanka bore out these findings: lorises there moved together in groups of up to nine).

Ultimately, I identified more than twenty individuals in an area about the size of thirty football fields. The boldest and most personable of these animals I named Titania; she was the one that taught me the most about loris behavior. Recognizable even from a distance, she was conspicuous because of her unique habit of treating branches like uneven parallel bars. Her ripe age was evidenced by multiple healed wounds and by very long nipples (an indication that she had given birth several times). Titania was courted by several of the local male lorises, who evidently found her as charming as I did. She commonly fed and played with various males, but none of them could challenge her--two or three swift cuffs were enough to subjugate any of them. Titania always got first access to large, juicy insects, and she always decided whether grooming would be reciprocated. Such primacy, however, was not just a product of Titania's personality; I soon learned that all female lorises, both in India and in Sri Lanka, dominate their male counterparts--a rarity in the primate world.

By the third month of the study, male interest in Titania escalated, for she went into heat. Reproduction is one of the few areas of loris behavior that has been well studied, albeit in captivity, but it turns out that behavior in the wild holds few surprises. Female lorises are capable of mating for a couple of days once or twice a year. Pregnancy lasts six months. Studies of captive lorises have shown that after a female has given birth, the demands of lactation and raising an infant may keep her from mating again for ten to fourteen months. Female slender lorises begin reproducing at two and often die in their mid-teens. They may mate as few as seven times in their lives--a limitation that creates severe competition among males, which constantly court females in hopes of mating during the brief time that one of them is in heat. Although in most primate species, fathers and other adult males do not play an important role in infant care, multiple male lorises studied at both the Indian and the Sri Lankan sites lavished attention on the young. Perhaps these males were showing choosy females what good fathers they would be, or even what good fathers they were (or thought they were). But I carried out no genetic studies during my trips to the field, so I don't know which animals were related or which males fathered which young.

In December 1997, during the rainy season, the male lorises of the Eastern Ghats lined up for a chance at Titania. She was typically imperious and cuffed three males before choosing the dominant male of the area: Donald. Quite a Casanova, he had been courting three or four local females, including one who already had a young son (although males hang around multiple females, it is difficult to say whether they mate with more than one). I have observed only four matings in the wild; Titania and Donald's was one of these. Lorises hang upside down from a horizontal branch during copulation. The reason for this is a mystery, but captive animals not provided with the necessary perch will not reproduce. Sex lasts up to fifteen minutes. Donald and Titania copulated several times over three hours, but not without distraction. Despite being chosen, Donald had to fight off three other males to maintain his position. Unwanted but unwilling to accept defeat, and whining loudly from neighboring trees whenever the couple was copulating, the three rivals attacked Donald one at a time. Several rather nasty fights broke out, accompanied by loud chittering and growling. The scene was reminiscent or a barroom brawl. Donald won each time, throwing the other males out of the tree, while Titania played the coquette, daintily stuffing herself with insect truffles.