Loris tardigradusslender loris

Geographic Range

Loris tardigradus (the slender loris) is a strepsirhine primate restricted to the island of Sri Lanka. (Campbell, et al., 2011; Phillips, 1980; Schulze and Meier, 1995a)


Three subspecies of L. tardigradus and one subspecies of its only congener, Loris lydekkerianus, maintain fairly discrete habitat niches in Sri Lanka. Loris tardigradus tardigradus is found in wet, lowland forests of the southwest. Loris tardigradus grandis occupies the central hills ranging from 731 m to 1036 m in elevation and is thought to interbreed with L. t. tardigradus at middle elevations in the extreme west of its range. Loris tardigradus nycticeboides is a rare montane form known only from its type locality in mist forests of the Horton Plains at elevations of greater than 1500 m. A subspecies of gray slender loris, Loris lydekkerianus nordicus, inhabits the lowland dry forests and scrub jungle of the north. Some authors consider grandis and nycticeboides to be subspecies of Loris lydekkerianus (see Groves, 1998). This account follows the taxonomic account in Campbell et al. (2011). (Campbell, et al., 2011; Groves, 1998; Phillips, 1980; Schulze and Meier, 1995a)

  • Range elevation
    0 to 2134 m
    0.00 to 7001.31 ft

Physical Description

Loris tardigradus is a small (127 g - 256 g) primate with long, gracile limbs, a slender body, and no tail. Its face is characterized by prominent ears, a short rostrum, and large, forward-oriented eyes with hazel-brown irises. Distinctive patches of dark fur surround the eyes, and a white stripe runs from forehead to nose. The coloration of circumocular patches and the shape of the interocular stripe are used to distinguish subspecies. The rostrum is sharply pointed and ends in a moist, naked rhinarium. Slender loris ears (both L. tardigradus and L. lydekkerianus), are longer than those of slow lorises (genus Nycticebus), and the margins of the ears are usually hairless. Females have two pairs of mammae which are naked during lactation and covered with fur at all other times. Limbs are subequal as the legs are bulkier and slightly longer than the arms. The palms of the hands and the soles of the feet are usually naked. As in other strepsirhine primates, there is a toilet-claw on the second digit of both feet. Their hands are smaller than their feet, and the index finger is reduced. Digits close synchronously, with the hallux and pollex opposable to digits two through five. Like Nycticebus, and in contrast to Perodicticus, Loris species have a hairless brachial gland on the inside of the arms. This gland produces an exudate important in olfactory communication, which may also have an anti-predator function. The basal metabolic rate of Loris tardigradus is not known, but lorises in general have slower metabolisms than would be expected from their body size. Research indicates a BMR of 0.38 (ml O2/g * hr) for their close relative, L. lydekkerianus malabaricus. (Alterman, 1995; Campbell, et al., 2011; Hagey, et al., 2007; Izard and Rasmussen, 1998; Macdonald, 2001; McNab, 1984; Müller, et al., 1985; Napier and Napier, 1967; Nekaris and Stevens, 2007; Nowak, 1999; Phillips, 1980; Schulze and Meier, 1995a; Schulze and Meier, 1995b)

Three subspecies of L. tardigradus are recognized and can be distinguished by size and pelage characteristics. Loris tardigradus tardigradus is the smallest slender loris, weighing from 128 g to 142 g and with a head-body length not exceeding 206 mm. Dorsal pelage is red to reddish-brown, darkest on the shoulders and paler on the lower back and pelvis. The fur of the lower back may be slightly frosted, but less so than Loris tardigradus grandis. A dark-colored dorsal stripe is sometimes present, but never as conspicuous as that of Loris lydekkerianus nordicus. Ventral fur is yellowish. Patches around the eyes are chestnut colored, and the interocular stripe rarely bifurcates above the eyes. Females are larger than males and have a brown color, with little or no red. Infants are gray dorsally and white ventrally. Subadult males have female-like coloration and gradually become more red. Loris tardigradus grandis is larger than L. t. tardigradus, has a less delicate appearance, and is more heavily furred, especially on the limbs. It weighs up to 227 g and has a head-body length between 209 mm and 256 mm. Dorsal fur is gray and ventral fur is white. Frosting is much more pronounced than in L. t. tardigradus. The circumocular patches are black or dark brown, and the interocular stripe bifurcates and merges into white fur surrounding the ears. Females are bigger, darker, and more frosted than males. Juveniles are brown and do not have frosting. Loris tardigradus nycticeboides is known only from a few specimens. Its mean weight is 140 g, and its head-body length ranges from 204 mm - 213 mm. The fur is considerably longer than that of the other subspecies, with ventral hairs as long as 30 mm. Dorsal pelage is brown and the ventral pelage is buff. Patches around the eyes are black, and the narrow interocular stripe bifurcates and continues around the eye patches. This subspecies is unique in that the ears are completely furred. The hands and feet are also notably hairier than those of the other subspecies. (Phillips, 1980; Schulze and Meier, 1995a)

  • Sexual Dimorphism
  • female larger
  • sexes colored or patterned differently
  • Range mass
    127 to 227 g
    4.48 to 8.00 oz
  • Range length
    185 to 256 mm
    7.28 to 10.08 in
  • Average basal metabolic rate
    0.714 W


Little is known of the mating habits of Loris tardigradus in the wild. A number of behaviors described in L. lydekkerianus have not been confirmed in L. tardigradus, and much of the available data (for either taxon) comes from captive individuals. Both species are reported to form social associations in which the larger home ranges of one or more males overlap the smaller range of a single female. Loris tardigradus tardigradus has been observed to gather in semi-stable sleeping groups of one female, her offspring, and a single male; groups with multiple males are reported for L. lydekkerianus. In both taxa, the presence of a post-copulation vaginal plug of hardened semen has been reported. This, along with elaborate penile morphology, has been taken as evidence of sperm competition and a multi-male breeding system. Nekaris (2003) observed several wild male L. lydekkerianus rotating among three estrus females, with each male separately grooming each female at different times over the course of a single night. Nekaris (2003) proposes a multi-male, multi-female (i.e., promiscuous) mating system. (Campbell, et al., 2011; Dixson, 1995; Izard and Rasmussen, 1985; Macdonald, 2001; Napier and Napier, 1967; Nekaris, 2003; Nowak, 1999; Schulze and Meier, 1995b)

Observations of captive Loris lydekkerianus populations indicate no reproductive seasonality, but this may not be true in the wild. It has been suggested that Loris tardigradus breed biannually, peak birth times for L. lydekkerianus in India occur during April and May and from October to December. May-December birthing schedules have been reported in Sri Lanka as well. Short-term field studies found no evidence for seasonality in wild populations of either Loris speices and documented one instance of a female L. lydekkerianus in estrus while her close neighbors carried infants. Testis of both taxa switch frequently between the scrotal and inguinal (i.e., descended and undescended) conditions, and no pattern of male genital change has been discovered with respect to female estrus or time-of-year. Enlargement of male genitals appears to be affected by ambient temperature rather than sexual activity, with enlargement occurring during increased temperatures. (Campbell, et al., 2011; Izard and Rasmussen, 1985; Nekaris, 2003; Nowak, 1999; Schulze and Meier, 1995b)

Courtship by male Loris tardigradus consists of a lengthy pursuit of the female, with threat vocalizations and appeasement vocalizations. It is not clear which role, threatener or appeaser, each gender assumes. Researchers have been unable to observe the entire courtship process, and no copulations have been witnessed. Mating behavior in L. tardigradus appears to be similar to that in L. lydekkerianus nordicus, which can last for five hours and is characterized by appeasement vocalizations and excited branch-shaking on the part of the male, and threat vocalizations by the female. In captive L. lydekkerianus, when the female is ready for copulation she communicates her acceptance by adopting a suspensory posture (i.e., hanging quadrupedally on the underside of a branch). Intromission lasts from two to sixteen minutes and is concluded by a threat vocalization from the female. Both genders lick their genitals after copulation. A single copulation of L. lydekkerianus has been documented in the wild, which was preceded by an hour-long courtship pursuit and occurred in a suspensory position under a horizontal branch. Males in other trees harassed the mating pair, and copulation was twice interrupted while the focal male chased away his rivals. (Campbell, et al., 2011; Izard and Rasmussen, 1985; Nekaris, 2003; Nowak, 1999; Schulze and Meier, 1995b)

Gestation in Loris tardigradus lasts 166 to 175 days, and females give birth to a maximum of two litters per year that usually consists of single offspring. Occasionally, a female may give birth to twins. Females are known to reenter estrus while nursing a previous litter. Infants are altricial, clinging to their mothers continuously for the first four weeks of life. After four weeks, young are placed in a sheltered location during active nighttime periods. Weaning takes place around 185 days, by which time the juveniles have achieved adult size. (Campbell, et al., 2011; Izard and Rasmussen, 1985; Nekaris, 2003; Nowak, 1999; Schulze and Meier, 1995b)

  • Breeding interval
    Loris tardigradus breeds twice a year
  • Breeding season
    None confirmed
  • Range number of offspring
    1 to 2
  • Average number of offspring
  • Range gestation period
    167 to 174 days
  • Average weaning age
    185 days
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    380 days
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    365 days

Little information exists concerning reproduction in slender lorises. The entire process, from copulation to independence of offspring, takes at least 320 days, and females may become pregnant with a new litter before weaning previous young. Physiological costs of lactation are high, as females produce milk with unusually high fat and protein content compared to that of other strepsirhine primates. Sexually mature females make a substantial caloric investment in reproduction throughout the year, but more research is needed to quantify this investment and to explore its implications for feeding ecology, social systems, and patterns of parental care. (Campbell, et al., 2011; Izard and Rasmussen, 1985; Izard and Rasmussen, 1998; Nekaris, 2003; Schulze and Meier, 1995b; Tilden and Oftedal, 1997)

At birth, Loris tardigradus infants are helpless. They instinctively cling to their mother's fur and remain there day-and-night for at least four weeks. After four weeks, lorises "park" their young in dense tangles of branches during nighttime foraging activity. Research indicates that L. lydekkerianus, a close relative of L. tardigradus, mothers abandoned their offspring for the entire night, and that parked infants were sometimes played-with and groomed by males. Although the relationship of males to infants is unknown, individuals who babysat in this way belonged to the same sleeping group as the mother. This behavior is probably a form of affiliative paternal care. The assistance of males in nighttime parenting may give lactating mothers increased mobility when foraging, helping them to satisfy their high caloric expenses. In contrast, L. tardigradus infants are not visited by males, and females returned to parked young as frequently as once per hour during the night. (Campbell, et al., 2011; Izard and Rasmussen, 1985; Izard and Rasmussen, 1998; Nekaris, 2003; Schulze and Meier, 1995b; Tilden and Oftedal, 1997)

Rare cases of infanticide have been reported for captive Loris tardigradus. Such instances are always said to be accompanied by "environmental stress", and do not appear to be directed by males toward the offspring of other males. There are no reports of infanticide in wild populations of L. tardigradus. (Campbell, et al., 2011; Izard and Rasmussen, 1985; Izard and Rasmussen, 1998; Nekaris, 2003; Schulze and Meier, 1995b; Tilden and Oftedal, 1997)

  • Parental Investment
  • altricial
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
  • post-independence association with parents
  • extended period of juvenile learning


There is no information available on the longevity of Loris tardigradus in the wild. One captive individual reportedly lived 15.5 years. (Nowak, 1999)


Slender lorises are nocturnal and arboreal. Their movements are famously slow, fluid, and noiseless. Tests on captive animals indicate normal speeds of about 0.59 m/sec. Lorises are, however, capable of rapid climbing and noisy episodes of branch-shaking. A recent field study by Nekaris and Stevens (2007) found "rapid quadrupedalism" to be surprisingly common in slender lorises. This scrambling mode of locomotion is qualitatively different from hand-over-hand climbing, and is used about 26% of the time. During this form of movement, individuals reach speeds approaching 1.2 m/s. Slender lorises may be capable of "mini leaps", but they usually move from tree to tree by careful cantilevering, which involves grasping a vertical branch with their hindlimbs and extending its body horizontally across the gap. Hip, ankle, and wrist joints are very mobile (Napier & Napier, 1967), and precarious postures can be maintained for extended periods because retia mirabilia supply the limb muscles with oxygen and remove cellular waste, preventing cramping. Lorises typically travel on the tops of branches, and they prefer climbing structures (e.g., branches or vines) small enough to be grasped in their hands. Individuals in a captive grey slender loris colony showed extreme care when negotiating smooth vertical trunks 10 cm in diameter. In the same colony, bipedal standing to the tops of branches and bipedal hanging by the hindlimbs underneath branches were both repeatedly observed, however, bipedal hanging by the forelimbs was rare. (Campbell, et al., 2011; Napier and Napier, 1967; Nekaris and Stevens, 2007; Nowak, 1999; Phillips, 1980; Schulze and Meier, 1995b)

During the day, slender lorises aggregate in sleeping groups which include a single adult female, her offspring, and one or more males. These associations may be stable from night to night, and adult males in a sleeping group may participate in parental care. Both in captivity and in the wild, slender lorises participate in social cohesion behaviors such as huddling, allogrooming, play-wrestling and play-biting. A variety of vocalizations, in addition to body language and elaborate olfactory communication are utilized. In captivity, grey slender lorises openly steel food from each other without provoking hostility. Although aggression captive populations is not uncommon, most aggressive behavior in the wild has been described between unrelated adult females and between males who do not belong to the same sleeping group. Nighttime activities reported for slender lorises consists primarily of travel and foraging, but also includes social activities, including those between mother and young, and rest. (Campbell, et al., 2011; Nekaris, 2003; Schulze and Meier, 1995b)

  • Range territory size
    15,900 to 36,000 m^2

Home Range

Although no information is available concerning home range in Loris tardigradus, average home range for L. lydekkerianus males is 3.6 ha (36,000 m^2) and 1.59 ha (15,900 m^2) for females. (Campbell, et al., 2011; Nekaris and Stevens, 2007)

Communication and Perception

There is no information available regarding communication and perception in slender lorises.

Slender lorises call to one other throughout the night, and on several occasions even directed vocalizations at potential predators. The known vocal repertoire of slender lorises consists whistles, chitters, zic calls, krik calls, growls, and screams. Whistle indicate excitement and aggression and consists of one to three distinct syllables, each ending with a descending frequency sweep. Utilized by males and females, whistles are always loud, and may be audible to humans from 100 m away. Evidence suggests that whistles are most prevalent in wild populations, possibly because long distance communications are unnecessary in captivity. In captivity, whistling in one cage provoked response vocalizations from groups caged nearby. Chitter are used as a defensive threat and are sometimes associated with staring or physical shoving. Primarily uttered by females, chitters are often used in response to a courtship pursuit by a male. Chitters consist of rapid clicks at frequencies up to 20 kHz. Zic calls consist of high frequency monosyllables that are used by an infant to attract the attention of its mother. Parked infants often zic-call, at which point the mother returns from foraging and collects the infant. Low intensity zic calls may be utilized when an infant dislikes grooming, but high intensity calls signify fear or pain. In captivity, adults other than the mother may comfort a zic-calling infant. Krik calls are a hiss-like, low frequency sound used by males to appease chittering females and are commonly used by males as a prelude to allogrooming. Females use krick calls to appease zic-calling infants. Sometimes male-female duets are performed using krik calls. Growl are an unvoiced threat vocalization that are used against predators, or by captured animals. Rarely uttered in intraspecific contexts, growls are most often used in connection with defensive body language. Screams are used in circumstances of prolonged threat and are associated with secretion of exudate from the brachial gland. (Nekaris, 2003; Nekaris, et al., 2007; Schulze and Meier, 1995b)

Like many mammals and most nocturnal primates, slender lorises make extensive use of scent markings to communicate information. Urine marking are made by rhythmic micturition (a stereotyped behavior in which the animal travels along a branch and deposits urine at intervals by rhythmically lowering its genitals to the substrate), anogenital dragging, and indirect application (urine applied to the substrate via the hands or feet of the urinating individual). Self-washing with urine is regularly observed in a variety of contexts, including before grooming infants prior to nightly parking, when preparing to catch noxious insects, prior to consuming noxious prey items, and in response to being stung by them. Urine marking is rarely observed in the vicinity of trees used for sleeping, but marks at localities within the range-overlap area shared by sleeping-group members were eagerly received and countermarked. Scent communication also plays a role in immediate social behavior. Anogentical sniffing (male to female) often precedes grooming, and grooming bouts frequently involve rubbing and licking of the brachial gland. (Alterman, 1995; Nekaris and Stevens, 2007; Schulze and Meier, 1995b)

Slender lorises use a variety of communicative postures, actions, and facial expressions indicating aggression, submission, contentment, fear, sexual intention (male), sexual readiness (female), and other kinds of socially relevant information. Through allogrooming and huddling, touch plays an important role in establishing and maintaining group cohesion. It may also help orient them in the dark. (Schulze and Meier, 1995b)

Food Habits

Slender lorises are primarily insectivorous, specializing to some extent on toxic and unsavory species. Particularly noxious insects are eaten with evident distaste, and insects which spray irritant chemicals are removed from their colonies and eaten some distance away, while the loris salivates gratuitously, shakes its head, and shuts its eyes. Evidence suggests that volatile chemicals ingested with insect food might be reused by lorises as a kind of olfactory camouflage. Foraging lorises are frequently observed wash themselves in urine before approaching toxic insects, perhaps in order to mask their own scent. The hunting style of slender lorises and other lorises is to approach silently and cautiously, then to make a sudden explosive grab with one or both hands. Predation behavior of slender lorises has been described as a fixed action pattern that begins with visual fixation of the prey, followed by laying back of the loris' ears, and concluding with the grasping motion, which is always completed regardless of whether or not the prey item is removed. In the wild, nearly 100% of the diet is proteinaceous and includes insects, tree frogs, geckos, small birds and eggs. They may occasionally forage on fruit when available. In captivity, slender lorises are fed green salads and plantains, and readily consume mice. (Campbell, et al., 2011; Macdonald, 2001; Napier and Napier, 1967; Nekaris and Stevens, 2007; Nekaris, et al., 2007; Nowak, 1999; Phillips, 1980; Schulze and Meier, 1995b)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • eggs
  • insects
  • Plant Foods
  • leaves
  • fruit
  • flowers


There are few known predators of Loris tardigradus. They may occasionally be opportunistically taken by mammalian carnivores including felids and raptors. It has been reported that genets and civets prey on lorises, but in several interactions observed by researchers between lorises and civets (Viverricula indica majori, Paradoxurus zeylonensis) or cats (Felis viverrinas), lorises simply whistled until the potential predator moved away. It is not clear if the whistle functions as a warning to conspecifics, or as a pursuit deterrence signal to the predator. Loris tardigradus females and their infants react with alarm to the presence of venomous common kraits and moved to a sheltered location until the snake has passed. When captured by researchers, lorises perform a defensive behavior which resembles that of indian cobras, which are present throughout the geographic range of L. tardigradus. When captured, L. tardigradus raises its arms above its head and sways its slender body side to side. (Alterman, 1995; Hagey, et al., 2007; Krane, et al., 2003; Schulze and Meier, 1995b)

The brachial glands of slow lorises (Nycticebus) secrete volatile chemicals which can be toxic to humans. It is not clear whether these compounds function as a poison or an alarm pheromone, but secretion of a pungent-smelling exudate from the brachial gland is a common result of fear in both slow and slender lorises. Alterman (1995) hypothesized that volatiles in the brachial gland do not become active until they are mixed with saliva, and performed preliminary tests suggesting that mammalian carnivores such as clouded leopards, binturongs, and sun bears respond with extreme aversion to brachial gland exudate when it is mixed with loris saliva, but not when it is presented alone. Other researchers identified proteins in the brachial exudate with regions of 70% sequence similarity to a known felid allergen. No studies have investigated the composition or function of brachial gland exudate in slender lorises, but L. tardigradus may be protected from predation by virtue of unpalatability. (Alterman, 1995; Hagey, et al., 2007; Krane, et al., 2003; Schulze and Meier, 1995b)

  • Anti-predator Adaptations
  • mimic

Ecosystem Roles

There is no information available regarding the ecological role of slender lorises. They prey heavily on insects, but they are not common anywhere and it is doubtful that they control populations.

Economic Importance for Humans: Positive

Slender lorises are illegally hunted exploited for traditional medicine and for the pet trade. (Nekaris, 2010)

  • Positive Impacts
  • pet trade
  • body parts are source of valuable material

Economic Importance for Humans: Negative

Loris bites may induce shock in humans and are often slow to heal. However, wild lorises are extremely shy of contact and do not attack humans unless provoked. No other adverse effects of Loris tardigradus on humans are known. (Alterman, 1995)

  • Negative Impacts
  • injures humans
    • bites or stings

Conservation Status

Loris tardigradus is considered endangered by the IUCN's Red List of Threatened Species and is listed under Appendix II under the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Major threats to their persistence include habitat loss, hunting for the pet trade and for their meat, road kills, superstitious kills, and traditional medicine. In his Manual of Sri Lankan mammals, W.W.A. Phillips wrote that L. tardigradus, "is most difficult to discover unless the jungle in which it lives is being felled." Habitat destruction is a serious threat to all three L. tardigradus subspecies, and the survival of the species depends on the enforcement of their protections throughout 7 different nature preserves in Sri Lanka and the establishment of corridors between protected areas. ("Appendices I, II, and III", 2010; Nekaris, 2010; Phillips, 1980)


Rory McGuinness (author), University of Michigan-Ann Arbor, Phil Myers (editor), University of Michigan-Ann Arbor, John Berini (editor), Animal Diversity Web Staff.



uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and