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.
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.
Communication Channels: visual ; tactile ; acoustic ; chemical
Other Communication Modes: scent marks
Perception Channels: visual ; tactile ; acoustic ; chemical
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.
US Federal List: no special status
CITES: appendix ii
State of Michigan List: no special status
There are no known adverse effects of Loris lydekkerianus on humans.
Body parts of grey slender lorises are illegally sought for traditional medicine, with no proven efficacy.
Positive Impacts: body parts are source of valuable material
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).
Commensal/Parasitic Species:
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.
Animal Foods: amphibians; reptiles; insects; terrestrial non-insect arthropods; mollusks
Plant Foods: fruit; sap or other plant fluids
Primary Diet: carnivore (Insectivore )
Grey slender lorises are found in southern India and in central, north-central, and east-central Sri Lanka.
Biogeographic Regions: oriental (Native )
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.
Habitat Regions: tropical ; terrestrial
Terrestrial Biomes: forest ; rainforest ; scrub forest
Other Habitat Features: agricultural
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.
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.
Range mass: 180 to 290 g.
Average length: Females: 23.4; Males: 24.1 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
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.
Known Predators:
Anti-predator Adaptations: cryptic
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.
Mating System: polygynandrous (promiscuous)
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.
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.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
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.
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)
