Loris lydekkerianusgray slender loris

Geographic Range

Grey slender lorises are found in southern India and in central, north-central, and east-central Sri Lanka. (Nekaris and Jayewardene, 2004; Radhakrishna and Singh, 2002; Schulze and Meier, 1995; Singh, et al., 2000)


Grey slender lorises survive in a wide variety of habitats including dry forest, wet forest, montane forest, rainforest, and scrub forest. Within these habitats, the ideal environment for this largely arboreal species contains plentiful oblique and horizontal surfaces for climbing, feeding, and mating. Grey slender lorises are found in many ecological zones including wet zones, low dry zones, and low country zones. The range of Loris lydekkerianus has been expanded to an unknown extent due to the careless collection and distribution of plant materials. Grey slender lorises are sometimes inadvertently transported with plant materials. (Kumara, et al., 2005; Nekaris and Jayewardene, 2004; Nekaris, 2003a; Radhakrishna and Singh, 2002; Schulze and Meier, 1995; Singh, et al., 2000)

Physical Description

Grey slender lorises have grey or reddish dorsal pelage with a darker medial stripe and a white ventrum. Their distinctly forward facing eyes are large and set closely together, while the rostrum is small and pointed. The coloring of the face is also distinctive; they have circumocular patches, darker preauricular hair, and a white rim between the circumocular patch and preauricular hair. Grey slender lorises have no tails and the limbs are long and extremely slim. Male weight ranges from 180 to 290 grams, depending on the subspecies. Female weight ranges from 180 to 275 grams. The average male length is 24.1 cm and the average female length is 23.4 cm.

There are four subspecies: Loris lydekkerianus lydekkerianus, L. l. grandis, L. l. malabaricus, and L. l. nordicus. These different subspecies differ in geographic location, pelage, and size.

Loris l. lydekkerianus has gray body color, a narrow circumocular patch, and a broad white rim between the dark preauricular hair and circumocular patch. The subspecies is generally larger in mass, with males weighing approximately 260 grams and females weighing 275 grams. The head length, body length, and head breadth are larger in L. l. lydekkerianus than in L. l. malabaricus.

Loris l. malabaricus has a reddish body color, a broad circumocular patch, and a narrow white rim between the dark preauricular hair and circumocular patch. Both male and female adults weigh approximately 180 grams.

Loris lydekkerianus has many distinctive derived characteristics including extremely slender limbs, the closest orbital approximation of all primates, small hands in comparison with the feet, feet with shortened second digits, a unique non-saltatory locomotor style, digestive specializations for ingesting toxic prey, and an unusually low basal metabolic rate. The species also exhibits retia mirabilia of the proximal limb vessels, an adaptation that allows for extended periods of arboreal clinging.

Grey slender loris appearance changes significantly throughout its development. Infants (4 to 8 weeks) have fluffy, large heads relative to body size. Juveniles (2 to 3 months) have particularly fluffy pelage all over the body, and adults (4 months onward) exhibit full body size and complete adult coloration patterns. External genitalia is also present in adults, with estrous females displaying enlarged genitalia, and male testes alternating between descended and inguinal stages every other night. In Loris lydekkerianus, no pattern has been observed with respect to male testes state and sexual activity. However, in the closely related slender loris (Loris tardigradus), enlargement of male genitals appears to be affected primarily by ambient temperature, with testes enlargement occurring during periods of increased temperature. Lastly, Loris lydekkerianus females have two sets of nipples, a feature that proves useful when females give birth to twins. (Kumara, et al., 2006; Nekaris, 2003b; Nekaris, et al., 2008; Schulze and Meier, 1995; Singh, et al., 1999)

  • Sexual Dimorphism
  • male larger
  • Range mass
    180 to 290 g
    6.34 to 10.22 oz
  • Average length
    Females: 23.4; Males: 24.1 cm


Grey slender lorises have a polygynandrous mating system. Females mate with multiple males within a single estrous cycle and can mate with multiple males in a row. Males mate with multiple females throughout the year. The female estrous cycle lasts for 24 hours, and gestation periods are approximately 165 days. The interbirth interval lasts approximately 7 months, and the female reproductive potential is 4 infants per year. This relatively high reproductive potential may be due to male allocare and the high-energy milk provided by the mother. Mating behaviors of grey slender lorises are highly social; an estrous female is physically pursued by multiple males at a time. Males display interest in estrous females by increasing grooming frequency, emitting more frequent vocalizations, and by following the female. Males follow foraging females for long periods of time, anywhere from one to dozens of hours. During this period, females can physically deter the trailing males with physical cuffs. Male-male competition can occur between males trailing the same female. These confrontations involve vocalizations such as growling, chittering, and whistling. Male-male competition can also be physically violent involving chasing and grappling. The most successful male competitor is normally permitted mating privileges by the female. If a female permits mating, copulation occurs with the female suspended on a horizontal branch. Single mating intromissions last anywhere from 3 to 11 minutes. A complete sexual encounter often consists of several individual mating intromissions, and can last for up to 12 hours. Depending on the outcomes of male-male competition, different males can mate with the same female consecutively. Studies of captive animals show that male ejaculation is associated with male pelvis wiggling and the insertion of a “copulatory plug” into the female that serves to block the mating success of other males. Females have been observed removing and consuming the copulatory plug. (Nekaris, 2003b; Nekaris, 2003a; Radhakrishna and Singh, 2004a)

The reproductive seasonality of grey slender lorises is disputed. Some researchers claim that the most frequent estrous periods occur biannually, in April to June and October to December. Others claim that births are distributed throughout the year, and that any apparent reproductive peaks are simply a result of the 5.5 month gestation length. Males reach sexual maturity at approximately 10 months, while the age of female sexual maturity has been estimated from 10 to 15 months. Grey slender lorises give birth equally frequently to single young and twins. The timeline of infant development is largely shaped by the ‘parking’ behavior demonstrated by females. For the first 4 weeks of life, infants are carried all the time by the mother. Approximately 4 weeks after birth, mothers begin to ‘park’ infants at night before leaving to forage. The exact timing of the onset of this parking behavior is likely related to the parenting experience of the mother. Grey slender loris females rarely return to their infant before dawn when they are parked. (Nekaris, 2003b; Radhakrishna and Singh, 2004b; Radhakrishna and Singh, 2004a)

  • Breeding interval
    Grey slender lorises breed once every 5.5 months.
  • Breeding season
    Grey slender lorises breed throughout the year.
  • Range number of offspring
    1 to 2
  • Average gestation period
    5.5 months
  • Average weaning age
    5 months
  • Average time to independence
    4 months
  • Range age at sexual or reproductive maturity (female)
    10 to 15 months
  • Average age at sexual or reproductive maturity (male)
    10 months

Though grey slender lorises have a polygynandrous mating system, they demonstrate both female parental care and male allocare behaviors. Males provide allocare only to infants that share their sleeping sites, but the genetic relationship between these males and infants is unknown. Female allocare is rare; females almost exclusively care for their own infants in the form of feeding, carrying, grooming, and protection. Female parental investment is intensive during infancy. Mothers groom infants exhaustively for the first three days after birth, and after this period groom only upon infant vocalization. Mothers constantly carry their infants during the first 4 weeks of life. At 4 weeks, infants are ‘parked’ near the sleeping site at night while the mother forages. Mothers also provide unusually high-energy milk before weaning, which occurs at approximately 5 months of age. Male allocare is common. While infants are parked, mothers almost never return until dawn. During this time, males and subadult males often visit parked infants, sometimes grooming or playing with the infants. The genetic relationship between visiting males and parked infants is unknown, though the males observed playing with infants are always members of the infant’s sleeping group. Males regularly groom both the mother and offspring during infancy. (Nekaris, 2003b; Nekaris, 2003a; Radhakrishna and Singh, 2004b)

  • Parental Investment
  • precocial
  • male parental care
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-independence
    • protecting
      • male
      • female


The lifespan of grey slender lorises and other lorisid species have not been widely researched. However, closely related slender lorises has a maximum lifespan of 16.4 years and Sunda slow lorises have a maximum lifespan of 26.5 years. (Conn, 2006)


Grey slender lorises are nocturnal. Other loris species are almost completely solitary, but Grey slender lorises and slender lorises are unique in their regular social interactions. During the day, grey slender lorises almost always sleep in social groups of 2 to 7 individuals that are most frequently composed of an adult female, her offspring, and a small number of adult or subadult males. The location and composition of these sleeping groups are generally constant. The sleeping site is typically centrally located within the home range of the primary female. Sleeping sites are generally located in cacti or tangled branches. Individuals sleeping together usually form a “sleeping ball” congregation in which individuals tangle their limbs together. At dusk, the sleeping site members wake and groom one another, with grooming occurring between individuals of all ages and sexes. Behavioral data about sleeping site composition and home range patterns supports the hypothesis that slender lorises have a multi-male social system. During nighttime foraging, grey slender lorises are generally solitary, though amicable foraging pairs have been observed. Males and subadult males often visit parked infants during the night. In general, social interactions occur between adult males and females, as well as between adults and juveniles, but rarely occur between adults of the same sex. Grey slender lorises and the slender lorises spend up to half of their time in the presence of other individuals. Research on activity budget has also shown that the species spends approximately 45% of its time engaging in inactive behaviors such as sitting, vigilant watching, resting, and sleeping. The rest of the activity budget is spent foraging or traveling and a small percentage is spent grooming. The most common positional behaviors are sitting and quadrupedal movement. A slow, crypic, non-saltatory locomotor pattern is considered characteristic of the family Lorisidae. However, the slender lorises are the only species within the family that have also been observed moving quickly; the slender loris species have been seen running and engaging in short jumps, though these kinds of fast movements are rare. The generally slow speed and silent motions protect the species against detection by predators that rely on visual or auditory cues. For this reason, particularly slow movements are used while moving across open ground between discontinuous substrates. The slow locomotor strategy also aids in food acquisition; particularly slow movements are used immediately before catching fast moving insect prey. (Nekaris, 2001; Nekaris, 2003b; Nekaris, 2003a; Nekaris, 2001; Nekaris, 2003b; Nekaris, 2003a)

  • Range territory size
    11,200 to 36,000 m^2

Home Range

The range of adult males is 2.36 to 3.6 ha, with a central, core range size of 0.37 ha. The range of adult females is 1.12 to 1.59 ha, with a core area size of 0.15 ha. Juvenile males have an average home range size of 1.17 ha. Until 10 months old, young grey slender lorises remain within their mother’s home range. Female adults have little intrasex overlap in their home ranges, while males have large intrasex overlap. Any intrasex range overlap is limited to peripheral range areas, and core areas remain exclusive to one individual. Intersex range overlap is common and can include core areas. A single male’s home range can overlap with the home ranges of multiple females. The average density within grey slender loris ranges is 2.4 lorises per km^2. (Nekaris, 2003a; Radhakrishna and Singh, 2002; Radhakrishna and Singh, 2004a)

Communication and Perception

Unlike most members of the family Lorisidae, grey slender lorises are relatively gregarious. The species maintains social networks with frequent loud calls throughout the night. Loud calls are also used when potential predators are detected, during reproduction, and during infant care-taking. Males interested in estrous females use more frequent vocalizations while following females. Male-male competition also includes complex growling, chittering, and whistling. Females emit these same noises when chasing away unwanted suitors. Additionally, parked infants will emit “zic" sounds approximately thirty minutes before dawn to alert the mothers of their location. Micturition, or urination, is another important method of communication. The species uses rhythmic micturition and urine washing as methods of territorial olfactory marking. Urine washing has also been observed as a stress response. Such olfactory behaviors are used for social communication. Slow lorises have keen low-light vision because of their nocturnality. Prey is detected primarily by vision and smell. (Ilse and Raschke, 1955; Nekaris and Rasmussen, 2003; Nekaris, 2001; Nekaris, 2003b; Nekaris, 2003a)

Food Habits

Loris lydekkerianus is almost entirely insectivorous, and more than half of its diet is composed of ants and termites. Grey slender lorises also consume a large variety of other arthropods, including other insects, such as beetles and orthopterans, spiders, mollusks, and occasional small vertebrates. Many prey species contain toxic chemicals. The consumption of toxic species is accompanied by an elaborate behavioral repertoire including sneezing, head shaking, sucking of the hands and feet, and urine-washing. Rarely, individuals eat tree gum by scraping the surface of hardened tree gum with their toothcombs to access the soft exudate beneath. In captivity, slender lorises consume a variety of small animals including insects, small mammals, and geckos. Prey is detected primarily by vision and smell. The most common hunting behavior involves visual or olfactory detection, ear retraction, noticeable sniffing, and a meticulously slow approach. Most frequently, one hand holds onto a substrate while the other hand hovers near the prey before quickly darting forward and grabbing the prey in a sudden burst of motion. Occasionally, these lorises catch prey bimanually or will directly consume prey with the mouth. One individual was observed repeatedly allowing termites to climb onto its saliva-coated hand, trapping them in the saliva before licking them off. Large prey are eaten head-first and any wings are typically removed before consumption. The majority of feeding events involve food items found in patches such as insect aggregations. This pattern has implications about the unusually gregarious and social nature of the species. Loris lydekkerianus is most frequently found near trees with heavy orthopteran leaf damage and near trees associated with ant colonies. Additionally, population density is positively correlated with insect density. (Kumara, et al., 2005; Nekaris and Jayewardene, 2004; Nekaris and Rasmussen, 2003)

  • Animal Foods
  • amphibians
  • reptiles
  • insects
  • terrestrial non-insect arthropods
  • mollusks
  • Plant Foods
  • fruit
  • sap or other plant fluids


The reaction of Loris lydekkerianus to predators has not been widely studied. However, the species has been observed reacting to potential predators by emitting loud calls, fleeing, or maintaining a large distance from the threat. Spotted owlets (Athene brama) have been noted as one potential predator of grey slender lorises. Though these birds are too small to prey upon adults, infant slender lorises move to safer, more unexposed locations upon hearing the call of spotted owlets. Domestic cats (Felis catus) have been noted as occasional predators of grey slender lorises. Humans (Homo sapiens) trap and hunt grey slender lorises as well. (Nekaris, 2001; Nekaris, 2003b)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Grey slender lorises impact insect populations through predation. Because ants and termites compose the majority of the slender loris diet, these insects are particularly affected. Two new parasitic species have been discovered in Loris lydekkerianus: Giardia wenyoni is found in the duodenum of grey slender lorises (Abraham, 1962a) and Trichomonas tardigradi in the intestine (Abraham, 1962b). Additionally, research performed before the phylogenic differentiation of Loris tardigradus and Loris lydekkerianus identified two nematode parasite species in an unspecified slender loris subspecies: Physaloptera masoodi was located in the stomach of the slender loris subspecies and Subulura indica in the appendix (Krishnamoorthy et al., 1978). (Abraham, 1962a; Abraham, 1962b; Krishnamoorthy, et al., 1978; Kumara, et al., 2005; Nekaris and Rasmussen, 2003)

Commensal/Parasitic Species
  • Giardia wenyoni
  • Trichomonas tardigradi
  • Physaloptera masoodi
  • Subulura indica

Economic Importance for Humans: Positive

Body parts of grey slender lorises are illegally sought for traditional medicine, with no proven efficacy. (Nekaris and Jayewardene, 2004)

  • Positive Impacts
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of Loris lydekkerianus on humans.

Conservation Status

Loris lydekkerianus is classified as Least Concern on the IUCN Red List of Threatened Species due to its “wide distribution, tolerance of a broad range of habitats, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category” (Nekaris et al. 2008). However, the species is also listed as Data Deficient on the IUCN Red List, for significant areas considered to be in the distributional range of the species remain unexplored. Additionally, research about its distribution follows no standard method, often leading to misleading or inconsistent status estimations. The subspecies Loris lydekkerianus nordicus and Loris lydekkerianus grandis are listed as Endangered on the IUCN Red List, while Loris lydekkerianus malabaricus and Loris lydekkerianus lydekkerianus are listed as Near Threatened. Loris l. malabaricus and Loris l. lydekkerianus are the two Indian subspecies of grey slender lorises. Loris l. malabaricus is found throughout the Western Ghats in a contiguous population. There are several protected forest tracks within this distributional range. Loris l. lydekkerianus is distributed in patches in southeast India. There are no protected forest areas in its range. This subspecies faces serious conservation challenges because it largely occurs in areas owned by commercial plantations. In general, the ranges of all Loris lydekkerianus subspecies are affected by habitat destruction specifically caused by human encroachment. The destruction of primary and secondary forest, the reduction of forest cover, the use of forest for agriculture, and the formation of fragmented forest patches impede the success of the Grey Slender Loris. The species is also threatened by hunting and trapping for use in traditional medicine. A reduction in habitat loss, the establishment of corridors between fragmented forest patches, and greater anti-hunting efforts are necessary for the continued survival of the grey slender lorises. Because of their sensitivity, grey slender lorises do not breed well in captivity, making their conservation in the wild a particularly urgent concern. (Kumara, et al., 2006; Nekaris and Jayewardene, 2004; Nekaris, 2003b; Nekaris, et al., 2008)

Other Comments

Grey slender lorises were once classified as Loris tardigradus lydekkerianus, a subspecies of Loris tardigradus. In 2001, this taxonomy was updated based on behavioral, geographic, and morphological data. Loris lydekkerianus is now considered a separate slender loris species found in India and Sri Lanka, while Loris tardigradus is a slender loris species found exclusively in Sri Lanka. Both slender loris species are unique among the members of the family Lorisidae in many respects. The species are unusually social, sleeping in groups and regularly interacting with other individuals during nighttime foraging. The species also occasionally exhibit fast locomotion, which has not been observed in other species of Lorisidae. Lastly, the slender loris species are uniquely gregarious, emitting loud contact calls throughout the night. (Groves, 2001; Kumara, et al., 2006)


Abi Nishimura (author), Yale University, Eric Sargis (editor), Yale University, Rachel Racicot (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



uses sound to communicate


living in landscapes dominated by human agriculture.


Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


An animal that eats mainly insects or spiders.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


found in the oriental region of the world. In other words, India and southeast Asia.

World Map


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


Living on the ground.


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born


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Abraham, R. 1962. On two new species of Giardia parasitic in Indian mammals. Parasitology, 53: 159-164.

Conn, M. 2006. Species Selection in Comparative Studies of Aging and Antiaging Research. Pp. 14 in Handbook of Models for Human Aging. Burlington, MA: Elsevier Academic Press.

Groves, C. 2001. Primate Taxonomy. Washington, D.C.: Smithsonian Institution Press.

Ilse, D., K. Raschke. 1955. Olfactory marking of territory in two young male loris, Loris tardigradus lydekkerianus, kept in captivity in Poona. The British Journal of Animal Behaviour, Volume 3, Issue 3: 119-120.

Krishnamoorthy, R., K. Srihari, H. Rahaman, G. Rajasekjaraiah. 1978. Nematode parasites of the slender loris, Loris tardigradus. Animal Sciences, 87(3): 17-22.

Kumara, H., S. Kumar, M. Singh. 2005. A Novel Foraging Technique Observed in Slender Loris (Loris lydekkerianus malabaricus). Feeding on Red Ants in the Western Ghats, India. Folia Primatologica, Volume 76: 116-118.

Kumara, H., M. Singh, S. Kumar. 2006. Distribution, habitat correlates, and conservation of Loris lydekkerianus in Karnataka, India. International Journal of Primatology, Volume 27, Issue 4: 941-969.

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Nekaris, K. 2001. Activity budget and positional behaviour of the Mysore slender loris: Implications for slow climbing locomotion. Folia Primatologica, 72(2): 228-241.

Nekaris, K. 2003. Observations on mating, birthing and parental care in three subspecies of slender loris in the wild (Loris tardigradus and Loris lydekkerianus). Folia Primatologica, Volume 74: 312-333.

Nekaris, K. 2003. Spacing system of the Mysore slender loris (Loris lydekkerianus lydekkerianus). American Journal of Physical Anthropology, Volume 121: 86-96.

Nekaris, K., J. Jayewardene. 2004. Survey of the slender loris (Primates, Lorisidae Gray, 1821: Loris tardigradus Linnaeus, 1758 and Loris lydekkerianus Cabrera, 1908) in Sri Lanka. Journal of Zoology, Volume 262: 327-338.

Nekaris, K., D. Rasmussen. 2003. Diet and feeding behavior of mysore slender lorises. International Journal of Primatology, 24: 33-46.

Radhakrishna, S., M. Singh. 2002. Home range and ranging pattern in the slender loris (Loris tardigradus lydekkerianus). Primates (Japan), 43: 237-248.

Radhakrishna, S., M. Singh. 2004. Infant development in the slender loris (Loris lydekkerianus lydekkerianus). Current Science, 86(8): 1121-1127.

Radhakrishna, S., M. Singh. 2004. Reproductive Biology of the Slender Loris (Loris lydekkerianus lydekkerianus). Folia Primatologica, 75: 1-13.

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Singh, M., M. Kumar, H. Kumara, S. Mohnot. 2000. Distribution and Conservation of Slender Lorises (Loris tardigradus lydekkerianus) in Southern Andhra Pradesh, South India. International Journal of Primatology, 21(4): 721-730.

Singh, M., A. Udhayan, M. Kumar, H. Kumara, D. Lindburg. 1999. Status survey of slender loris Loris tardigradus lydekkerianus in Dindigul, Tamil Nadu, India. Oryx, 33: 30-36.