GRAY SLENDER LORIS

Loris lydekkerianus

Geographic Distribution and Habitat

The gray slender loris is endemic to the eastern and western Ghat mountains of southern India and the island nation of Sri Lanka. These prosimian primates (the oldest, most “primitive” group of primates) have been geographically categorized into four distinct subspecies. The Malabar gray slender loris (Loris lydekkerianus malabaricus) and the Mysore gray slender loris (Loris lydekkerianus lydekkerianus) are native to India, while the northern gray slender loris (Loris lydekkerianus nordicus) and highland slender loris (Loris lydekkerianus grandis) are found in Sri Lanka. 

The subspecies found in India reside in the arid and higher altitudes of the eastern and western Ghat mountains. Even though it’s a mountainous region, this habitat would be described as a tropical dry forest. They also have been found to occupy flatter subtropical regions near plantations, as well as agriculturally cultivated areas near taller forests.

The two other subspecies are found in the dry-zone forest areas of northern and central Sri Lanka. A dry-zone forest is made up of mostly evergreen trees, distinguishing it from other regions of tropical lowland forests. These subspecies’ distribution rates are significantly smaller and more restricted. 

Gray slender loris geographic distribution, IUCN 2020

Size, Weight, and Lifespan

The gray slender loris is not large in size. On average, all four subspecies measure at about 7.75-9.4 in (20.5-23.8 cm) in body length, and can weigh between .18 and .35 lbs (85-150 g). They have relatively small limbs at an average length of 1.65-2.15 in (4.91-5.46 cm). Their lifespan has not been widely researched, but based on lifespans of other related slender lorises, it is believed that they can live up to 16 years in the wild and perhaps up to 26 years in captivity.

Appearance

Despite their name, each gray slender loris subspecies varies in color. The subspecies found in India typically have thick grayish-brownish fur along their backs with cream coloring along the underside and around the face. Dark brown or black colors surround their distinctively large amber-brown eyes.

The Sri Lankan subspecies have darker reddish coats, with a cream-colored underside. Their darker face is heart-shaped and their ears are not as visible through their thicker fur.

All subspecies lack a prominently visible tail. They have long, slender limbs and fingers. Their thumbs are widely separated from the rest of their hand, giving them a strong sturdy grasp that facilitates hunting and mobility. They have small, comb-like teeth with tilted incisors in the lower jaw.

Diet

Gary slender lorises have an almost entirely insectivorous diet composed of ants and termites. They also consume a large variety of other arthropods, including other insects such as beetles, mollusks, spiders, and the occasional small vertebrate.

They use their long slender fingers to forage for insects within trees and insect hives. The most common hunting behavior is through visual detection, sniffing, smell, and ear retraction. They tend to have a very slow, meticulous approach to foraging. They use their strong grip with one hand to hold onto a branch or surface and the other to extract or grab the insect, crushing it in their hand. Researchers have observed them directly consuming prey, rather than killing before consumption.

Diet plays a large role in the population density of these primates. There is positive correlation between density of gray slender lorises to density of insect populations. Basically, where there are more insects or large insects hills, there are more gray slender lorises. While this may seem obvious, it shows that they do not always travel far distances to find food; rather, they nest or stay closer to areas with more insects.

Behavior and Lifestyle

Gray slender lorises are nocturnal primates, meaning they are most active at night. Most loris species are completely solitary, however, the gray slender loris is highly socially active. During the day, they sleep in social groups of up to seven. They form what researchers have called a “sleeping ball” or “sleeping pod,” where they connect limbs and tangle up.

During dusk hours they groom each other, which forms social bonds. This behavior is observed in several other species of primates. Play between juvenile members of the group is common and includes jumping, chasing, and vocalizations. 

Social activity is observed between adult males and females and between adults and juveniles, but hardly between adults of the same sex. This is most likely due to competition or group dynamics and group roles. 

Fun Facts

Females lay upside down during mating.

Gray slender loris completely ‘freeze’ when in danger. 

Daily Life and Group Dynamics

Daily life for these small prosimians is comprised of foraging, social play, inactivity, and traveling. They spend up to half of their time in each other’s presence and less than half of their time inactive, while the rest of their time is spent traveling for food and grooming. More often than not, adult males and females will go off and forage alone at night, while males periodically return and check up on the parked juveniles, as they do not forage for themselves until maturity is reached around the age of 10-15 months. They have been observed occasionally traveling and foraging in pairs, which suggests that, from time to time, they are able to maximize food collection in pairs.

They live in a multi-male social system, which means that there is more than one male present in each group. Groups are made up of about seven individuals, which include offspring, at least one female, and at least a pair of adult males. 

The gray slender loris is not monogamous, which means that they participate in a mating system in which they have more than one mating partner. During the few active times throughout the day and evening, the females spend part of the time looking after the newborn, who are dependent upon them for the first 10 weeks after birth. 

Communication

The affably social gray slender loris keeps up its social behavior through repeated loud calls throughout the night. These calls range from steady pitched “whoops” to lower pitched “growls.” These calls are social in nature, strengthening social bonds, and also are meant to gauge location. The social networking of the gray slender loris is not Twitter, but is their loud and persistent calls to one another!

Gray slender lorises also use these whoops and higher pitched screams to alert the group to predators. They are not fast-moving animals, so they depend on these alarm calls to avert potential danger.

Males competing with each other for females use a series of aggressive vocalizations such as growling, chittering, and whistling. When a female decides she is uninterested, she emits these vocalizations to the males. When a male follows a female he is sexually interested in, he will use consistent vocalization patterns to try and draw her attention.

Even the young have a complex system of vocalizations that mean certain things. At nighttime just before dawn, a juvenile emits a loud “zic” sound to alert the mothers of their whereabouts. They also vocalize playful noises while playing with one another or while being groomed.

The vocalizations and specific meanings of certain calls suggest that the communication system of the gray slender loris is very intelligent and complex. 

Many nocturnal primates rely on olfactory senses and cues. Researchers presume that, like other lorises, the gray slender loris uses brachial gland secretions to mark home territory and travel routes.  

Reproduction and Family

The gray slender loris has a polygynandrous mating system, meaning that both males and females have multiple breeding partners within a breeding season. Researchers disagree on when or if there is a specific breeding season, but there is a general consensus that females have a gestation period of about 5.5 months. Females have the potential to birth up to 4 children per year. 

Mating behaviors between males and females are social behaviors. A male shows interest in a female by increasing grooming frequency, sounding more frequent vocalizations, and following the female. Males often follow a foraging female for hours. Competition between males following the same female occurs. Confrontational vocalizations such as “growls” often occur between competing males. Physical violence between males such as chasing has also been observed. When a female permits a male to mate with her, the sexual encounter lasts from around 3-11 minutes. Oftentimes a female take on consecutive partners, meaning that when one male is done copulating another will immediately follow. Mating sessions can last up to 12 hours.

Most mothers give birth to one single infant or to twins. There is an equal probability that they will have either 1 or 2 offspring. Mothers have two sets of nipples, which especially help them if they must feed twins and possibly other youths. For the first four weeks of life, infants cling to their mothers. After four weeks, mothers begin to leave their young at the nesting site at night. It is then the males’ responsibility to check on the young throughout the night. Researchers have concluded that adult males only check on youths that are in the same sleeping ball as them, which strengthens the social significance of their sleeping patterns. They reach maturity at around 10-15 months, with females reaching sexual maturity quicker. 

Photo credit: Joachim S. Müller/Flickr/ShareALike license
​Ecological Role

The gray slender loris impacts insect populations due to its insectivorous diet and foraging. The populations of certain insects are very much affected by the amount of gray slender lorises present in the area. They are still a part of the food web, and can be hunted and eaten by larger predators in their habitat.

Conservation Status and Threats

The International Union for Conservation of Nature Red List of Threatened Species records that overall the gray slender loris is of Near Threatened (IUCN, 2020).

The species has a wide distribution, tolerance of a broad range of habitats, and is presumed to have a large population. However, it is facing threats from deforestation and/or hunting across its range, and although the species has a wider distribution in India than in Sri Lanka, suspected declines due to various threats in the two countries indicates that the species is not Least Concern as it was previously thought to be. The population is suspected to be declining, but at a rate approaching, but not yet meeting, the threatened category thresholds.

The primary threat is habitat loss. Other threats include road kills, electrocution on uninsulated power lines, capture for pet trade and use in traditional “medicine,” and killing due to superstitious beliefs.

Unlike other members of the loris family, the gray slender loris is not as popular in the illegal pet trade. Researchers have observed cases of humans hunting them near urban populations, however. Their proximity to urban areas make them susceptible to dangerous highways and unprotected power lines. Their ability to live in commercial agricultural fields and plantations makes them susceptible to farmers harvesting their crops. They have also been reported to be hunted and used for traditional medicine in the Tamil Nadu region of India, although research has concluded that there is no scientific foundation for them to be used medicinally.

Conservation efforts must balance trying to preserve populations while respecting local culture and tradition. Gray slender lorises do not breed well in captivity due to their sensitive disposition, so figuring out how to preserve wild populations is a concern for researchers.

Conservation Efforts

Where the population is more threatened in Sri Lanka, researchers are surveying new areas of forest in search of the gray slender loris. Finding populations in previously unpopulated areas creates a better, more exact distribution map. Maps like this determine which areas of forest need protection from development and deforestation. 

Hotel Jetwing Vil Uyana, a resort in central Sri Lanka, spotted populations of the highlander gray slender loris near one of their development sites and immediately stopped construction and funded the area to be a conservational site. They have set an example for how the commercial industry can help this primate, rather than hurt it. 

Primate Conservation Project Sri Lanka is a nonprofit group that has done research and surveys to protect the gray slender loris, and has been funded by major institutions such as the National Zoo, Conservation International, and Disney Nature. Researchers in India have suggested that speed breakers be put in roads that run through important habitats. Tree bridges across busy roads have also been raised as a possibility to reduce risk of road kill. Further conservation is dependent on more research and a better understanding of the species.

​References:
  • Perera, M. S. J. (2008). A review of the distribution of grey slender loris (Loris lydekkerianus) in Sri Lanka. Primate Conservation23(1), 89-96.
  • https://www.arkive.org/gray-slender-loris/loris-lydekkerianus/
  • https://www.revolvy.com/main/index.php?s=Sri%20Lanka%20dry-zone%20dry%20evergreen%20forests&item_type=topic
  • http://animaldiversity.org/accounts/Loris_lydekkerianus/
  • ​Nekaris, A., Singh, M. & Kumar Chhangani, A. 2008. Loris lydekkerianus. The IUCN Red List of Threatened Species 2008: e.T44722A10942453. 
  • http://www.bbc.com/news/av/world-28365020/the-grey-slender-loris-conservation-success-in-sri-lanka
  • Nekaris, K.A.I. (2005) Foraging behaviour of the slender loris (Loris lydekkerianus lydekkerianus): implications for theories of primate origins. Journal of Human Evolution, 49: 289-300.
  • ​http://lemur.duke.edu/slender-loris/

Written by John DeVreese, February 2018. Conservation Status updated December 2020.