RED SLENDER LORIS

Loris Tardigradus

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Geographic Distribution and Habitat
The red slender loris, also known as the slender loris, the Sri Lanka slender loris, and the Sri Lanka wet zone slender loris, is endemic to 100 to 110 different locations throughout Sri Lanka’s southwestern wet zone. The region is referred to as the “wet zone” because it receives about 10 feet (3 m) of rain every year. 

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Red slender loris range, IUCN 2020

Size, Weight, and Lifespan
The red slender loris is the smallest of the slender lorises, with a weight of 3–6 ounces (85–172 grams) and a length of 4.5–6.5 inches (12–17 cm). Females are a little smaller than males and weigh between 3.5 and 5 ounces (103–148 grams).

They can live up to 18 years in the wild.

Appearance
Delicate white markings accentuate the heart-shaped faces of these prosimian primates. With thin hairless round yellow ears on top of the head, disproportionately large forward-facing brown eyes, and a thin long pink wet nose, red slender lorises look like plush toys covered in thick and soft reddish caramel color fur with creamy undersides. They have no tail. Their limbs are gracile and end with highly mobile wrists and ankles. Their tiny hands have flat fingernails and a shortened second digit; their feet have a grooming claw on the second digit. Because the big toe and thumb can be adducted 180 degrees from the other digits, these tiny creatures have an incredibly powerful grip.

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Photo credit: Dr. K.A.I. Nekaris/Creative Common

What Does It Mean?

Adduct:
(Of a muscle) move (a limb or other part of the body) toward the midline of the body or toward another part.

Gracile: 
Slender, thin.

Prosimians:
The most primitive of the primates. “Prosimian” means pre-monkey. The living (extant) prosimians are in the suborder Prosimii, ​which includes four families of lemurs, the bush babies (galagos), lorises and pottos, and the tarsiers.

Tooth-comb:
The incisors on the lower front jaw of some animals are grouped as if to form a comb. The tooth-comb is used by these animals to groom and clean their fur or hair.​

Visit the Glossary for more definitions

Diet
Red slender lorises feed exclusively on prey. They are skilled hunters who delight in eating geckos and lizards but also enjoy various insects such as moths, dragonflies, grasshoppers, and ants. Their forward-facing eyes are an advantage for hunting, since it allows them to see depth. They approach their prey very quietly and grasp it quickly with one or both hands.

Their digestive system is such that they can ingest toxic prey without becoming sickened by it.

Behavior and Lifestyle
These nocturnal primates are tree dwellers with an inability to leap, so they are rarely found on the ground. Their home range covers as much 6 acres (2.6 ha) for males and 9 acres (3.7 ha) for females.

To find prey and feed, they travel in the canopy by grasping multiple thin twigs, vines, or lianas at once with their hands and feet. The branches they grasp are less than 2 inches (5 cm) in diameter. They usually move slowly, but they can be extremely fast—much faster than other loris species, in fact—and reach a speed of 5.4 feet/second (1.65 m/sec), especially when a male is pursuing a female he is interested in.

They thrive in trees at least 45 feet (14 m) high, although they mostly stay at about 25 feet (8.5 m) above ground level. For their sleeping sites, they prefer trees with dense tangles, thick leaf cover, and tree holes. They avoid open areas where predators can easily spot them.

Fun Facts

Fossil studies indicate that the most ancient living primates are lorisiforms.

Lorises were discovered in 1770 and were thought to be similar to sloths because they appeared to be moving slowly.

Daily Life and Group Dynamics
During the day, red slender lorises retire to their sleeping trees in groups consisting of one adult female, one adult male, and one offspring. They disperse and forage alone at night. The rest of the time, they socialize, groom, play-bite, and play-wrestle.

Communication
Red slender lorises communicate through vocalizations. They can produce six different whistles—each with a specific function. A whistle can contain five phrases of descending tones. These allow the lorises to communicate their location, maintain contact with members of their group, attract a member of the opposite sex, convey their mood, or alert the group of the presence of a potential predator. They call more frequently when the moon is bright, perhaps because they feel more exposed to predators than when the night is dark. Other vocalizations include chitters, growls, and screams. Babies use a specific “zic” sound to call their mothers.

Body postures, like head cocking and facial expressions, are other ways they communicate with one another.

They also express themselves through scent-marking, either by squirting urine in different locations or by rubbing their specialized scent glands on branches to pass on messages to members of their group.

Reproduction and Family
Females go into estrus when they are approximately one year old and exhibit swelling, thereby signaling their readiness for courtship. To obtain the favors of a female, a male follows her, parks himself in a tree at a lower height than she is, and patiently awaits the time when he can join her for a grooming session. The two then engage in a high-speed pursuit in the trees, before feeding and grooming together.  Several males may pursue the same female and occasional fights do occur.

Females give birth after a gestation period of 167–175 days (over 5 and a half months). Their babies are tiny and only weigh about a sixth of an ounce (5 g). Females typically produce one infant, although they occasionally bear twins and can reproduce several times a year—in December or January, March, June, and July. The babies’ eyes remain shut for the first week of life, but infants are immediately able to grab their mothers’ fur.  Mothers carry their offspring on their backs or bellies for the first four weeks of life. During that time, they don’t really touch the babies with their hands but rather groom them with their tongue or tooth-comb, mostly during periods of rest. At bed time, males join in and groom both mothers and infants. When the infants are six weeks old, the mothers start parking them on trees while they hunt. They check on them from time to time and return to retrieve them at dawn. The youngsters usually move a few feet away from where they were parked and make little “zic” sounds so their mothers can find them. Adults and sub-adults show interest in parked infants and often stay near them or groom them.

Mothers nurse their offspring for 6 or 7 months and their milk is rich in fat and protein.

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Photo credit: Joachim S. Müller/Fllickr/Creative Commons

Ecological Role
There is no information regarding the ecological role of red slender lorises.

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Conservation Status and Threats
The red slender loris is listed as Endangered by the International Union for Conservation of Nature (IUCN, 2015), appearing on the IUCN Red List of Threatened Species.

The biodiversity of Sri Lanka is very rich, with many more flowering plants, amphibians, reptiles, and mammals than other countries in South Asia. However, the growing human population and decades of civil unrest have turned the wet zone, where red slender lorises live, into an endangered ecoregion in dire need of extensive conservation investment.

Red slender loris populations are distributed in small and isolated forest patches, even within the same forest reserve. Lorises fare best in forests with a rich biodiversity of trees, plants, and mammals and where trees are higher with a thick cover. The Kottawa Arboretum and Massmulla Proposed Forest Reserve still meet these criteria. Unfortunately, as of 2013, only 5% of the original rainforests of Sri Lanka remained and only 25% provides suitable habitat for the endangered red slender loris.

All populations are thought to be in decline. Combining the available information for the formerly recognized subspecies, fewer than 2,650 individuals remain in total. Fewer than 2,500 mature individuals remain, and the population continues to decline. 

The threats imposed by humans on Sri Lankan Loris include loss of habitat, degradation of habitat and fragmentation of these habitats due to agricultural expansion, urbanization, uncontrolled exploitation of forest products such as firewood, illegal encroachment, alien species invasion, and mismanagement by relevant authorities.  Further, lorises suffer electrocution and road kills.

This primate’s natural predators include golden palm cats, rusty spotted cats, fishing cats, brown fish owls, forest eagle owls, and Indian pythons. The red slender loris can also be victim of the pet trade or be killed for use in folk remedies or sacred rites.

Conservation Efforts
The red slender loris is listed on the Convention on International Trade in Endangered Species (CITES) Appendix II and is protected under the Fauna and Flora Protection Ordinance Act No. 2, 1937, and subsequent amendments. Therefore, some of the forests where the red slender loris lives are protected, such as Sinharaja World Heritage or Horton Plains National Park, but these areas only represent 16% of the remaining forests in Southern Sri Lanka. Because red slender lorises need rich diverse forests with tall trees and continuous canopy to travel, it is important to restore fauna and build corridors that link fragmented forest patches to ensure the survival of the species.

Working with the local population and government is equally important. Villagers in the wet zone understand the needs to protect the forest–especially for water preservation and to maintain a steady timber supply. Most villagers are Buddhists and do not harbor ill-feelings toward primates, nor do they eat them; they mostly rely on crops such as tea, rubber, rice, and bananas that do not get raided by red slender lorises because these animals feed on pray. These are positive factors for the protection of the red slender loris species.

It is important to note that the ZSL Edge of Existence program added the red slender loris to its list of global conservation priorities through a collaborative project called the Red Slender Loris Conservation Programme (RSLCP), which started in 2008.

References:

  • IUCN Red List​
  • Habitat quality and availability of the Sri Lanka Red Slender Loris (Loris tardigradus tardigradus) – (Mammalia: Primates: Lorisidae) in the Kottawa Arboretum – Saman Gamage, Wasantha Liyanage, Devaka Weerakoon & Asoka Gunwardena.
  • Influence of Forest Structure and Composition on Population Density of the red slender loris (Loris tardigradus tardigradus) in Masmullah Proposed Forest Reseve, Sri Lanka – K. Anne-Isola Nekaris, Wasantha K.D.D, Liyanage, Saman N. Gamage
  • Folia Primatol. 2003; 74:312-336 – Observations of Mating, Birthing and Parental Behavior in Three Subspecies of Slender Loris (Loris tardigradus and Loris Lydekkerianus) in India and Sri Lanka. – K.A.I. Nekaris
  • The Lorisiform Primates of Asia and Mainland Africa – Diversity Shrouded in Darkness – Anna Nears and Simon Bearder
  • Where Are They? Quantification, Distribution and Microhabitat Use of Fragments by the Red Slender Loris (Loris tardigradus tardigradus) in Sri Lanka – K.A.I. Nekaris and Carrie J. Stengel
  • Primate Conservation – The Journal of the IUCN/SSC Primate Specialist Group – Number 19, 2003
  • Journal of Anthropological Sciences – Vol. 91 (2013) – An ethnoprimatological approach to assessing levels of tolerance between human and commensal non-human primates in Sri Lanka – K. Anne-Isola Nekaris, Alex Boulton & Vincent Nijman
  • Evolutionary Anthropology 23: 177-187 (2014) – Extreme Primates: Ecology and Evolution of Asian Lorises – K. A. I. Nekaris
  • Habitat Use by the Red Slender Loris (Loris tardigradus tardigradus) in Masmullah Proposed Forest Reserve in Sri Lanka – Lilia Bernede, Simon K. Bearder and Asoka Gunawardene
  • American Journal of Primatology 69:112-120 (2007) – Not All Lorises Are Slow: Rapid Arboreal Locomotion in Loris tardigrade of Southwestern Sri Lanka – K.A.I Nekaris and N.J. Stevens
  • www.activewild.com 
  • www.zsl.org “Saving slender lorises in Sri Lanka”
  • www.edgeofexistence,org 
  • www.activewild.com
Written by Sylvie Abrams, October 2019. Conservation Status updated December 2020.