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Slow loris


The N. c. coucang social system might be closest to a monogamous single male/single female social system with the pair living with offspring (Wiens & Zitzmann 2003b; Nekaris & Bearder 2007). In one study, slow lorises (N. coucang) were predominantly solitary, spending only around 8% of their active period near other slow lorises. If an individual slow loris home range overlaps with that of another, encounters are generally friendly, but not so if there is no range overlap. These friendly relations define "spatial groups" which are a unit of social organization in the species. In general, only four types of interaction are seen on a nightly basis among slow lorises in the same "spatial group." These include allogrooming, following, pant-growling, and click-calling, and social behavior only make up around 3% of the activity budget (Wiens & Zitzmann 2003b). In captivity, allogrooming is also the most common social behavior (Newell 1971). In addition, not all individuals are members of a spatial group. Home ranges are not defended, and neither are food patches. When members of a spatial group encounter non-members, there is usually no interaction (Wiens & Zitzmann 2003b). While usually alone, adult slow lorises will sometimes sleep with up to several conspecifics, including other adult animals (Wiens 2002).

N. coucang
Nycticebus coucang
Photo: Andrew Johns

Social behaviors in varying contexts have been recorded in artificial groups of captive N. coucang. In fact, when kept together in captivity, they are quite sociable, although adult males can be very intolerant of one another and may fight, often resulting in serious injury (Ehrlich & Musicant 1977; Tenaza & Fitch 1984). In captivity, agonistic behaviors include attacks, pursuits, threats, assertion, fighting, and subordinate behaviors. Associative behaviors include close proximity, physical contact, following, social exploration, social grooming and social play (Ehrlich & Musicant 1997). In a different captive study, severe aggression included threats and attacks, and less intense aggression (staring, cringing, pant-growling and avoidance) was also seen (Daschbach et al. 1982-1983). Dominant or submissive behaviors among slow lorises are not seen in captivity (Rasmussen 1986).

In general, slow lorises disperse around 16-27 months of age, and both sexes have been seen dispersing in the wild (Wiens & Zitzmann 2003b).


The true mating system of wild slow lorises is unknown, and may in fact be variable between populations (Wiens & Zitzmann 2003b). However, it might be best described as a monogamous single male/single female social system (Wiens & Zitzmann 2003b; Nekaris & Bearder 2007). In one anecdotal observation, several male slow lorises were seen to follow a female and attempt to mate with her (Elliot & Elliot 1967).

N. pygmaeus females show sexual swelling during estrus, during which the genitals turn reddish. Females also show behavioral estrus, increasing their approach, departure, and lunge behaviors during estrus (Fitch-Snyder & Jurke 2003). N. coucang however, only rarely show these sexual swellings (Zimmermann 1989). Males pursue estrus females around (Fitch-Snyder & Jurke 2003). Estrus cycles in N. coucang last 29-45 days, averaging 36.4 days, with copulations mostly occurring on a single day (Izard et al. 1988). Copulatory plugs are sometimes seen after N. coucang reproduction (Izard et al. 1988). Females of N. pygmaeus and N. coucang solicit copulation by hanging from a branch (often making whistling vocalizations) and copulation occurs thus, with the male grasping both the female and the branch (Zimmermann 1989; Fitch-Snyder & Jurke 2003). N. coucang also solicit copulation by walking in front of the male and urine-marking and vocalizing (Zimmermann 1989). In captivity, N. pygmaeus are seasonal breeders, with most births occurring between January and April. In the wild, they also likely breed seasonally, although the actual timing and duration is unknown (Fitch-Snyder & Jurke 2003). Contrary to this, other species of slow loris are not seasonal breeders, and instead are polyestrous (Fitch-Snyder & Jurke 2003).

Successful reproduction can happen as early as 73 weeks in captive male N. pygmaeus and sexual maturity likely occurs before 14 months of age in males of the species, although actual reproduction usually occurs around 17-20 months old (Weisenseel et al. 1998; Fitch-Snyder & Jurke 2003). Female N. coucang are sexual mature between 17-24 months old (Izard et al. 1988; Weisenseen et al. 1998). Gestation lengths for N. coucang and N. pygmaeus are similar, averaging 191-192.2 days and 188.0 days respectively (Izard et al. 1988; Weisenseel et al. 1998).


N. coucang births are usually singletons, although twinning has been seen (Izard et al. 1988). N. coucang infants are born with open eyes and all of their fur, with gray face, limbs, and ventrum and a brown back with a dark stripe, and can cling to their mothers one hour after birth (Zimmermann 1989; Wiens 2002). Twins are more common in N. pygmaeus than in N. coucang (Fitch-Snyder & Ehrlich 2003). Birth weights in captivity average around 48.2 g (1.7oz), and the interbirth interval is around 16.2 months (Izard et al. 1988). In captivity, N. coucang first groom themselves at four weeks of age, and show first locomotion at around 6.2 weeks old, with drinking, eating and urine marking starting at 9.3, 12.0, and 13.0 weeks respectively (Ehrlich & Macbride 1989). However, in a different captive study, eating of solid food occurred much earlier, and development was described as being extremely quick, with infants showing adult movement and social patterns soon after birth (Zimmermann 1989). Infants are carried by clinging to the mother's fur on her ventrum, and are almost completely immobile in their first 6-8 weeks of age (Ehrlich 1974; Ehrlich & Macbride 1989). However, in the wild a four-week old infant (N. coucang) was seen to be able to climb about a food tree, albeit not adeptly (Wiens & Zitzmann 2003a). After the first week of life, mothers "park" their infants for prolonged periods, during which, the infants in many cases will not, or are unable to, follow (Ehrlich 1974; Tenaza & Fitch 1984; Ehrlich & Macbride 1989; Wiens 2002; Fitch-Snyder & Ehrlich 2003). From the second week on, infants follow their mothers (Fitch-Snyder & Ehrlich 2003). Wild N. coucang infants will only follow their mothers to a sleeping site (Wiens 2002). Between N. pygmaeus and N. bengalensis, mother-infant pairs of the former spend more time near each other, but overall, there are great similarities in the relationships between mothers and their infants across slow loris species (Fitch-Snyder & Ehrlich 2003). Overall, N. coucang maternal care consists only of suckling, carrying, and grooming (Wiens 2002). Maternal lactation persists around six months and weaning occurs between the fifth and seventh months of age (Izard et al. 1988; Zimmermann 1989).


N. coucang emits eight different types of call used in two basic functional groups, relating to contact or affiliation (including whistles, short keckers), and those relating to aggression and defense (including snarls, grunts, long keckers, and screams) (Zimmermann 1985). Slow lorises do not emit alarm calls (Wiens & Zitzmann 2003b). Whistle calls are often heard from females in estrus (Daschbach et al. 1981). Ultrasonic vocalizations out of the human hearing range, are emitted when slow lorises explore unknown environments and during handling (Zimmermann 1981). Infants emit click sounds when they are isolated from their mother and when they feel distressed (Rassmussen 1986). Click-calls are used as a method for individuals to reconvene at sleeping sites after nightly activity (Wiens & Zitzmann 2003b).


Slow lorises have a gland on their elbows that exude oils used in communication, of which the composition is particular to each species (Hagey et al. 2007). This secretion from the elbow glands probably evolved for communication, but can be toxic to humans if bitten, as licking is one mode for deposition of the scent. This is especially true among people who have had contact with the animals and may have developed allergies to them. Individuals have gone into shock and even died after slow loris bites (Wilde 1972; Hagey et al. 2007).

Olfactory communication is important in slow lorises, and they signal conspecifics by urine marking, and through deposition of scent from glands on their elbows and anus (Tenaza & Fitch 1984; Rasmussen 1986; Hagey et al. 2007). Rhythmic uriniation is one method of scent deposition in the species, in which the animal moves about and deposits urine as it moves (Rassmussen 1986). Facial rubbing on a substrate usually occurs in response to the scent of another slow loris (Rassmussen 1986). Olfactory communication is important in reproduction in slow lorises (Fisher et al. 2003a). N. pygmaeus males overmark the scent-marks of other males. N. pygmaeus urine-marking odor is individually distinguishable among the species, and females use marking and countermarks by males to assess the desirability of the males (Fisher et al. 2003a). Further, in captive experiments, females prefer males whose odor they are familiar with (Fisher et al. 2003b).

Postural and facial communication is not particularly common in slow lorises. However, two commonly seen postures/facial expressions are the grin and bare-teeth displays, both usually accompanied by vocalizations. Grins are shown by infants, usually when stressed. Bare-teeth displays involve showing the teeth, and are seen during agonism, but also during play behaviors (Rassmussen 1986).

Content last modified: March 18, 2009

Written by Kurt Gron. Reviewed by Helena Fitch-Snyder.

Cite this page as:
Gron KJ. 2009 March 18. Primate Factsheets: Slow loris (Nycticebus) Behavior . <>. Accessed 2020 July 6.