Animal Diversity Web

Geographic Range

Bengal slow lorises are endemic to the forested areas of south-eastern Asia, including the seven north-eastern states of India (Assam, Arunachal Pradesh, Mizoram, Nagaland, Meghalaya, Manipur, and Tripura) as well as areas of Cambodia, Burma, Thailand, Vietnam, and southern regions of China. The greatest densities of this species are found in eastern Thailand. They have the largest range and are the northernmost species of the genus Nycticebus. (Brandon-Jones, et al., 2004; Pliosungnoen, et al., 2010; Ravosa, 1998)

• Biogeographic Regions
• oriental
  • native

Habitat

Bengal slow lorises are nocturnal and arboreal strepsirrhines. They prefer areas of high canopy cover and forest edges, where insects are more abundant. They inhabit tropical and sub-tropical rainforests as well as semi-evergreen rainforests in southeastern Asia year round. However, with increasing destruction of their habitat due to deforestation and development of land, they are forced to live in scrub forest. Bengal slow lorises prefer larger and taller trees with deeper crowns that are associated with higher food abundance as well as a dense micro-habitat that provides protection from predators. They prefer older and younger plantation forests to primary forests and avoid habitats with shallow tree crowns. (Choudhury, 2001; Pliosungnoen, et al., 2010; Srivastava and Mohnot, 2001)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• rainforest
• scrub forest

• Range elevation

  0 to 2400 m

  0.00 to 7874.02 ft

Physical Description

Bengal slow lorises are the largest of all of the slow lorises, with a skull length of 65.25 mm, larger than any other species of loris. They are heavier than all other loris species with a mass between one and two kg and a length of 26 to 38 cm, being more than three times the weight of the smallest loris, Nycticebus pygmaeus. Bengal slow loris fur patterns differ from other slow lorises which allow for visual differentiation from other species. They have thick, wooly fur with a white head, neck, and underside and a brown-grey dorsal side accompanied by a slight darker brown dorsal stripe running down the back. They have a round head with short ears and rostrum and very large, stereoscopic eyes that have an orange-red eye-shine. They have very short, almost vestigial tails. There is no sexual dimorphism in Bengal slow lorises. Their hands are specifically designed for climbing and they have opposable thumbs that are significantly different from their other four phalanges, giving them a pincer-like grip. This strong grip makes up for their lack of a tail. Males and females look alike and can only be differentiated by looking at the gonads. Male Bengal slow loris testicles have an average weight of 1.2 grams, with a vas deferens length of 85.5 mm. The dental formula: I 2/2 C 1/1 P 3/3 M 3/3 = 36 (Fitch-Snyder and Schulze, 2001; Groves, 1998; Nekaris, et al., 2013; Smith and Jungers, 1997)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry
• venomous

• Sexual Dimorphism
• sexes alike

• Range mass

  1 to 2 kg

  2.20 to 4.41 lb

• Range length

  26 to 38 cm

  10.24 to 14.96 in

Reproduction

Once slow loris females are in estrus, they use a combination of urine marking and whistle calls to attract males in the area. The female will verify the male’s reaction to her calls by intermittently stopping and turning her head. The male will respond by sniffing her urine mark then urine marking on top. The male will then whistle back to her and approach her. She will assume a copulatory-invitation posture as she drops below a branch. After copulation, social grooming or social play may follow. A female may mate with multiple males throughout her 37 to 54 day estrus. Males also mate with multiple females. (Anderson, et al., 2004; Fitch-Snyder and Schulze, 2001)

• Mating System
• polygynandrous (promiscuous)

Information on reproduction in Bengal slow lorises is not reported in the literature. Their close relative, slow lorises, breed throughout the year. Once females conceive, they don't breed for the next two years as they invest highly in the maternal care of their young. They usually have one offspring, however twins have been reported. Mothers gestate for 176 to 198 days and give birth to precocial young that are covered in fur with their eyes open. Males and females are reproductively mature at around 1 to 1.5 years of age, however generally do not successfully conceive as soon as they are sexually mature. The mean age for first offspring birth in female slow lorises is 38.8 months, while males successfully produce offspring at a mean age of 50.6 months. Immediate postpartum estrus has been observed in slow loris mothers that have lost their young. When previous offspring survive at least six months and are mother-reared, the interbirth interval is 209 days. (Fitch-Snyder and Schulze, 2001)

• Key Reproductive Features
• iteroparous
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• viviparous
• post-partum estrous

• Breeding interval

  Bengal slow loris females probably breed every two years.

• Breeding season

  Bengal slow lorises probably breed throughout the year.

• Range number of offspring

  1 to 2

• Average number of offspring

  1

• Range gestation period

  176 to 198 days

• Range weaning age

  6 (low) months

• Range time to independence

  6 to 18 months

• Range age at sexual or reproductive maturity (female)

  1 to 1.5 years

• Range age at sexual or reproductive maturity (male)

  1 to 1.5 years

Members of the genus Nycticebus practice ‘infant parking,’ where they leave their young hanging from a tree while they go off to feed. Infants are able to be parked on the day of birth. Young are covered in exudates from their mother's brachial gland in order to protect them from predators. If an infant calls to the mother while parked, the mother will immediately return. Slow loris mothers and their infants have a close attachment from the time of birth, sometimes continuing through their lifetimes. They carry their young on their backs for as long as three months after birth. They spend a large amount of time play-wrestling and socializing with their mothers as well as other adults once a few months old. Fathers are absent after copulation and do not contribute to parental care. Infants can be weaned at 6 months, but will continue nursing until they reach sexual maturity. (Fitch-Snyder and Schulze, 2001; Nekaris, et al., 2013; Zimmermann, 1989)

• Parental Investment
• precocial
• female parental care
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female
• post-independence association with parents

Lifespan/Longevity

Limiting factors to the lifespan of Bengal slow lorises include predation by carnivores, environmental pressures, such as loss of territory, and anthropogenic causes, such as road kills and hunting. (Fitch-Snyder and Schulze, 2001; Radhakrishna, et al., 2010)

• Average lifespan
  Status: wild

  15 years

• Average lifespan
  Status: captivity

  20 years

Behavior

Lorises rarely exhibit aggression towards one another and usually live in family groups. Although some individuals are solitary, most live in a social setting. There is no dominance hierarchy in social groups. They travel 20 to 30 meters each night, either alone or in pairs. They often sleep in tree holes or dense vegetation, sometimes with other lorises, and may occupy up to 60 tree holes throughout their lifetime. They are tolerant of other loris species as they have been observed foraging on the same tree within meters of pygmy slow lorises which is sympatric with Bengal slow lorises. (Choudhury, 1992; Duckworth, 1994; Fitch-Snyder and Schulze, 2001; Pliosungnoen, et al., 2010; Radhakrishna, et al., 2006; Swapna, et al., 2010)

• Key Behaviors
• arboreal
• scansorial
• nocturnal
• motile
• sedentary
• solitary

Home Range

The home ranges of Bengal slow lorises overlap and vary in size. Their population density ranges from 1.27 to 4.26 individuals per square kilometer. This overlap is dependent on both number of competitors and the habitat quality of the area they occupy. (Swapna, et al., 2010)

Communication and Perception

High-pitched whistles are used to attract mates in Bengal slow lorises. Females use urine scent-marks to attract mates when in estrus. Chitters and clicks are used by infants to get their mother’s attention as well as to call her back when they are parked and the mother is out looking for food. Large stereoscopic eyes assist increase their vision at night as they are nocturnal. (Fitch-Snyder and Schulze, 2001)

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

Bengal slow lorises are generalized feeders consuming a diet of plant exudates, nectar, fruit, invertebrates, bark, and bird eggs. Their preferred food is dominated by plant exudates such as resins and gums from 6 species of plants which make up 94.3% of the diet in the winter, and 67.3% of their diet in the summer. An example of plant species consumed include Bauhinia as well as other liana species. Terminalia is also commonly consumed. Lorises obtain exudates using their procumbent incisors to gouge or scrape holes into the bark of trees. They then use their long, narrow tongues to scoop the exudates into their mouth. Nectar is the second preferred food with it consisting of 22.3% of their summer diet. (Pliosungnoen, et al., 2010; Swapna, et al., 2010)

• Primary Diet
• herbivore
  • eats sap or other plant foods

• Animal Foods
• eggs
• insects
• terrestrial non-insect arthropods

• Plant Foods
• wood, bark, or stems
• fruit
• nectar
• sap or other plant fluids

Predation

Bengal slow lorises use crypsis to prevent predator detection and often take cover in dense vegetation. When under attack by a predator, Bengal slow lorises roll up in a defensive posture with the brachial glands on the inside of their elbows over their heads to combine the brachial gland exude with saliva. This is applied to the head for defense and is likely foul-tasting. They also bite in defense using their procumbent teeth which can deliver this saliva into the predator. Humans can have allergic reactions to this substance because it is similar in structure to Fel-d1, also known as cat allergen. This can cause anaphylactic shock in humans and other predators. Many other volatile and semi-volatile compounds are also in the loris brachial gland exudates causing ill-effects in the predators. These secretions may also serve an anti-parasitic role, as lorises have an extremely low occurrence and intensity of ectoparasite infestation compared to other primates. Known predators of Bengal slow lorises include pythons (Python reticulatus), hawk-eagles (Spizaetus cirrhatus), and orangutans (Pongo pygmaeus). (Nekaris, et al., 2013; Rode and Nekaris, 2012; Utami and Van Hooff, 1997; Wiens and Zitzmann, 1999)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • pythons (Python reticulatus)
  • hawk eagles (Spizaetus cirrhatus)
  • orangutans (Pongo pygmaeus)

Ecosystem Roles

Bengal slow lorises serve as a host species for many internal parasites, such as Pterygodermatides nycticebi, Giardia species, Trichomonas species, and Physaloptera species. Some unspecified species of ticks may also be found in low quantities on some Bengal slow loris individuals. They are prey for many predator species. They serve as pollinators when feeding on the nectar of multiple flowers. (Fitch-Snyder and Schulze, 2001; Nekaris, et al., 2013; Pliosungnoen, et al., 2010)

• Ecosystem Impact
• pollinates

Economic Importance for Humans: Positive

Bengal slow lorises are commonly found as pets in households in southern Asia. They are sometimes used as food and in traditional "medicine," which has no proven value. (Radhakrishna, et al., 2010)

• Positive Impacts
• pet trade
• food

Economic Importance for Humans: Negative

Bengal slow lorises have a brachial gland on the ventral side of their elbow. This gland secretes substances that, when combined with saliva, may initiate an allergic response in humans, including potentially anaphylactic shock. One substance produced by the brachial gland is similar in structure to Fel-d1, also known as cat allergen. This could be the source for the anaphylaxis seen in humans. However, Bengal slow lorises are not aggressive and only bite in self-defense. (Nekaris, et al., 2013; Wilde, 1972)

Conservation Status

Before 2007, the species was considered Data Deficient on the IUCN Red List, stating that the lack of information on their distribution and status of the population could not lead to a definitive classification. However, in 2008 the IUCN Red List classified the Bengal Slow Loris as Vulnerable due to an expected 30% decline in the next three generations over the species’ entire range. This decline is attributed to increasing habitat destruction due to deforestation, hunting/poaching pressures, and road kills from increased traffic. The Bengal Slow Loris is also a large commodity in illegal animal trade markets for medicinal purposes, bush meat, and as pets. (Strietcher, et al., 2014)

• IUCN Red List

  Vulnerable

• CITES

  Appendix I

Other Comments

Bengal slow lorises were formerly considered one of four subspecies of Nycticebus coucang, their former taxonomic name being Nycticebus coucang bengalensis. Although there is minor gene flow between them, gene flow is limited and molecular testing and morphological characteristics suggest there is enough variation to call each slow loris their own species. Much of the literature still describes Nycticebus bengalensis as a subspecies of Nycticebus coucang. (Groves, 1998)

Contributors

Reyd Smith (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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