Animal Diversity Web

Ge­o­graphic Range

Pres­bytis thomasi is one of sev­eral lan­gurs found in the Ori­en­tal is­lands. How­ever, its ge­o­graphic range is fairly lim­ited. Its na­tive home con­sists of North Suma­tra of In­done­sia—more specif­i­cally, north of Sun­gai Wampu and Sun­gai Sim­pang Kiri. (Col­ijn and Muchtar, 1996; Nowak, 1999)

• Biogeographic Regions
• oriental
  • native

• Other Geographic Terms
• island endemic

Habi­tat

When search­ing through trop­i­cal rain­forests, rub­ber plan­ta­tions, and both pri­mary and sec­ondary forests, one is able to en­counter Thomas’s lan­gur. Since it is ar­bo­real, one usu­ally needs to search high in the trees to find this unique species. How­ever, its po­si­tion­ing in the trees de­pends on what time of day it is. While it is tak­ing a nap dur­ing the day, it se­lects a tree that tends to have lots of twigs and leaves for pro­tec­tion from the harsh sun­light. How­ever, when it is sleep­ing at night, it sleeps in the top of a tall tree that faces the open areas. (Col­ijn and Muchtar, 1996; Flan­nery, 2004; Gur­maya, 1986)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• forest
• rainforest

Phys­i­cal De­scrip­tion

Pres­bytis thomasi has a very dis­tinct ap­pear­ance. Due to their unique fa­cial col­oration, it is easy to dis­tin­guish North Suma­tran leaf mon­keys from other pri­mates. The white fur on the un­der­side and arms (which con­trasts with the black fur sur­round­ing the rest of the body) con­tin­ues up around the neck. Two other white stripes, start­ing from the top of the head, run down the sides, come to­gether in a V-shape at the eyes and en­cir­cle them. A pur­ple-sil­ver col­ored inner layer forms rings around the or­ange-brown eyes. In­side of the dark tint, one can see the pink­ish skin of Thomas's lan­gur. This same pink­ish skin cov­ers the muz­zle.

The av­er­age size of Thomas's lan­gur is 6.69 kilo­grams for adult fe­males and 6.67 kilo­grams for adult males. The tail length is be­tween 500 and 850 mm, and the head and body length ranges be­tween a mere 420 and 620 mm. (Col­ijn and Muchtar, 1996; Flan­nery, 2004; Nowak, 1999)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Range mass

  5 to 8.1 kg

  11.01 to 17.84 lb

• Range length

  92 to 147 cm

  36.22 to 57.87 in

Re­pro­duc­tion

The mat­ing sys­tem of P. thomasi is de­bated. In the En­cy­clo­pe­dia of Mam­mals, it is noted that the species is a monog­a­mous pri­mate. The fe­male ini­ti­ates the mat­ing by per­form­ing var­i­ous acts to per­suade her male coun­ter­part, such as re­leas­ing cer­tain smells and dis­play­ing gen­i­talia. ("Colobus and Leaf Mon­keys", 2001)

How­ever, oth­ers dis­pute the monogamy of the species. Steen­beck, et al. (1999) states that within groups, there are often sev­eral fe­males and one breed­ing male. A pos­si­ble res­o­lu­tion be­tween the two ob­ser­va­tions is that only one of the fe­males in the group breeds with the male while the other fe­males help raise the young. (Steen­beek, et al., 1999)

• Mating System
• monogamous
• cooperative breeder

There is no spec­i­fied breed­ing in­ter­val for Thomas’s lan­gurs. How­ever, even though the breed­ing sea­son is not re­stricted, there tends to be an in­crease in mat­ing when the fol­low­ing wean­ing pe­riod is ex­pected to cor­re­spond with an abun­dance of food. The ges­ta­tion pe­riod lasts 5 to 6 months. At the end of ges­ta­tion, fe­male P. thomasi pro­duce one young one young at a time. Fe­males rarely pro­duce more than one off­s­r­p­ing at a time, and never more than two. Wean­ing oc­curs at 12 to 15 months, after which an off­spring is sup­posed to be­come in­de­pen­dent. Al­though they are fully in­de­pen­dent, ju­ve­niles do not reach sex­ual ma­tu­rity until 4 or 5 years of age. ("Colobus and Leaf Mon­keys", 2001; Eimerl and De­Vore, 1965)

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

• Breeding interval

  Breeding can occur every 1.5 to 2 years.

• Breeding season

  The breeding season of these monkeys is not restricted.

• Range number of offspring

  1 (low)

• Average number of offspring

  1

• Range gestation period

  5 to 6 months

• Range weaning age

  12 to 15 months

• Range time to independence

  15 to 18 months

• Average age at sexual or reproductive maturity (female)

  4 years

• Range age at sexual or reproductive maturity (male)

  4 to 5 years

When car­ing for her young, the mother re­moves her­self from the dom­i­nance struc­ture. Other fe­males of the group are often at­tracted to the young due to the dis­tinct col­or­ing, and so they care for and pro­tect the young when­ever pos­si­ble. As soon as the in­fant be­comes upset or dis­traught, an­other fe­male quickly tries to com­fort it. The male in­fant has no con­tact with a male adult until he is 10 months old. Dur­ing pre-wean­ing, the young has to learn what to eat, what to avoid, and other be­hav­ioral tac­tics in order to sur­vive. ("Colobus and Leaf Mon­keys", 2001; Eimerl and De­Vore, 1965)

The male in­fant has no con­tact with a male adult until he is 10 months old. A fe­male in­fant, how­ever, has no con­tact with an adult male until she is 3.5 to 4 years old. Often dur­ing wean­ing, a male within the group or an out­side group com­mits in­fan­ti­cide, killing an in­fant so that the mother can re­gain her nor­mal cycle of fer­til­ity faster than she would if her child were still alive. This may ex­plain the delay in con­tact be­tween young and adult males. ("Colobus and Leaf Mon­keys", 2001; Eimerl and De­Vore, 1965)

• Parental Investment
• precocial
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female
• extended period of juvenile learning

Lifes­pan/Longevity

The av­er­age lifes­pan of P. thomasi is 20 years. In cap­tiv­ity, the av­er­age lifes­pan is 29 years. The nine-year dif­fer­ence may be due to nu­mer­ous fac­tors such as the de­struc­tion of habi­tat, hunt­ing by hu­mans, the pres­ence of nat­ural preda­tors, and at­tacks be­tween neigh­bor­ing groups. ("Colobus and Leaf Mon­keys", 2001)

• Average lifespan
  Status: wild

  20 years

• Average lifespan
  Status: captivity

  29 years

Be­hav­ior

These lan­gurs spend most of the day in groups ei­ther rest­ing, feed­ing, or mov­ing. These groups usu­ally con­sist of five fe­males and one male, but there can also be small groups of males or in­di­vid­ual males liv­ing alone.

Within these groups, there is a dom­i­nance hi­er­ar­chy that every­one, both male and fe­male, is sub­jected to. It has been sug­gested that an in­di­vid­ual’s rank within the hi­er­ar­chy may de­pend upon its age or its abil­ity to de­fend it­self against oth­ers in the group. ("Colobus and Leaf Mon­keys", 2001; Eimerl and De­Vore, 1965; Gur­maya, 1986; Steen­beek, et al., 1999)

Even though this lan­gur is known for hav­ing a calmer de­meanor in ges­tures and re­sponses to con­specifics than other pri­mates, com­pe­ti­tion has been ob­served within groups. Com­pe­ti­tion in­creases with the size of the group, and fem­laes show a pref­er­ence for smaller groups due to the de­crease in risk of in­fan­ti­cide. Group sizes are often de­pen­dent upon fe­male dis­per­sal. ("Colobus and Leaf Mon­keys", 2001; Steen­beck and van Schaik, 2001)

Many fac­tors im­pact a fe­male’s de­ci­sion to leave her group and join an­other. These in­clude com­pe­ti­tion for food, the risk of pre­da­tion, and avoid­ance of in­breed­ing. More im­por­tant is the avoid­ance of in­fan­ti­cide. Often a fe­male leaves her group to pro­tect her young from in­fan­ti­cide. (Sterck, 1997)

In­fan­ti­cide ap­pears to be a very im­por­tant be­hav­ior for P. thomasi. In­fan­ti­cide usu­ally oc­curs when males at­tack. Fe­males do not typ­i­cally at­tack un­less de­fend­ing their young from out­side males. Fe­males are much more ag­gres­sive when they have an in­fant than they are when they have no de­pen­dent off­spring. When the group male is within 5 me­ters of a mother and her child, she is sig­nif­i­cantly less vig­i­lant, ap­par­ently be­cause the pres­ence of the male so close by is an as­sur­ance of pro­tec­tion. (Steen­beek, et al., 1999)

• Key Behaviors
• arboreal
• scansorial
• diurnal
• motile
• nomadic
• territorial
• social
• dominance hierarchies

• Range territory size

  500 to 800 m^2

Home Range

Like most lan­gurs, P. thomasi is both di­ur­nal and ar­bo­real. It oc­cas­sion­aly re­trieves min­eral re­sources from the ground. Groups re­lo­cate to dif­fer­ent areas within the forests by mi­grat­ing through the trees. This so­cial species is also very ter­ri­to­r­ial, often de­fend­ing its area by bark­ing or even at­tack­ing out­siders. (Nowak, 1999)

Com­mu­ni­ca­tion and Per­cep­tion

Vocal com­mu­ni­ca­tion is at its most in­tense and fre­quent at dawn. It is uti­lized in a va­ri­ety of sit­u­a­tions such as re­lo­ca­tion, at­tack­ing, es­tab­lish­ing sleep­ing po­si­tions, de­fend­ing ter­ri­tory and mates. Vo­cal­iza­tions are ac­com­pa­nied by ol­fac­tory com­mu­ni­ca­tion when mat­ing is in­ti­ti­ated. ("Colobus and Leaf Mon­keys", 2001; Eimerl and De­Vore, 1965)

Thomas' lan­gurs use nu­mer­ous types of vocal calls. For ex­am­ple, an alpha male tends to make a se­ries of “choom” sounds when he is ex­cited; how­ever, when he is in­volved in an in­ter-troop or group-troop en­counter, he makes a se­ries of “kak” and “ngkung” sounds. Sim­i­larly, when threat­ened, ju­ve­niles make an al­ter­nat­ing se­ries of “kek”s and “wek”s. Ag­gres­sive fe­males make “kuk” sounds. (Gur­maya, 1986)

Vocal and vi­sual com­mu­ni­ca­tion de­velop as these mon­keys ma­ture. In in­fant P. thomasi, com­mu­ni­ca­tion is re­stricted to whin­ing and squeal­ing. Once an in­di­vid­ual be­comes a ju­ve­nile, its abil­i­ties have broad­ened to scream­ing, gri­mac­ing, slap­ping the ground, pre­sent, alarm bark­ing, star­ing, and threat bob­bing. Fi­nally, as an adult, it no longer squeals or screams, but barks and par­takes in dom­i­nance fight­ing. ("Colobus and Leaf Mon­keys", 2001; Eimerl and De­Vore, 1965)

As in all pri­mates, tac­tile com­mu­ni­ca­tion, be­tween mates, ri­vals, as well as be­tween moth­ers and their off­spring is im­por­tant. Tac­tile com­mu­ni­ca­tion in­cludes groom­ing, re­as­sur­ance, and ag­gres­sion.

• Communication Channels
• visual
• tactile
• acoustic
• chemical

• Other Communication Modes
• choruses
• pheromones

• Perception Channels
• visual
• tactile
• acoustic
• chemical

Food Habits

This leaf-mon­key’s diet is pri­mar­ily cen­tered around fruits, leaves, and seeds. How­ever, it will eat other things such as flow­ers, bark, twigs, stalks of co­conuts, leaf stalks, birds, bird eggs, algae, and some in­sects. Water is made avail­able in tree holes. Oc­ca­sional vis­its to the ground are made in order to ob­tain ants, toad­stools, soil, and snails. Large peaks in for­ag­ing occur three times per day, ac­com­pa­nied by rest­ing in the lower por­tions of trees. For­ag­ing be­hav­ior is highly in­flu­enced by the risk of pre­da­tion. (Flan­nery, 2004; Gur­maya, 1986; Nowak, 1999; Sterck, 2002; Swindler, 1998)

• Primary Diet
• herbivore
  • folivore
  • frugivore
  • granivore

• Animal Foods
• birds
• eggs
• insects
• mollusks

• Plant Foods
• leaves
• wood, bark, or stems
• seeds, grains, and nuts
• fruit
• flowers
• algae

• Other Foods
• fungus

Pre­da­tion

A char­ac­ter­is­tic shared among most of P. thomasi's preda­tors is the abil­ity to climb trees. Preda­tors such as retic­u­lated pythons, clouded leop­ards, tigers, and golden cats are often suc­cess­ful in cap­tur­ing Thomas’s lan­gurs. Be­cause these lan­gurs are able to move swiftly through branches, their preda­tors have been found to at­tack only when the dis­tance be­tween them and their prey is very short. Preda­tors are more ef­fec­tive when at­tack­ing P. thomasi on the ground rather than in trees. Be­cause of this, the most dan­ger­ous area for these mon­keys is in the lower strata of the for­est, which is 0 to 10m.

Thomas' lan­gurs rely on two valu­able forms of pro­tec­tion: their ar­bo­real habits and the alarm calls that are pro­duced when groups are around. Thomas’s lan­gurs climb down from trees more often when they are sur­rounded by neigh­bors.

Fe­males are more prone to pre­da­tion due to their pref­er­ence for snails and their smaller ca­nines. Males are often found nearby in trees look­ing out for preda­tors when fe­males ven­ture down to the ground by them­selves. (Flan­nery, 2004; Sterck, 2002)

• Known Predators

  • reticulated pythons (Python reticulatus)
  • clouded leopards (Neofelis nebulosa)
  • tigers (Panthera tigris)
  • Asiatic golden cats (Catopuma temminckii)

Ecosys­tem Roles

Be­cause of its pref­er­ence for fruits, flow­ers, and seeds, one can infer that P. thomasi may dis­perse seeds and help pol­li­nate plants while feed­ing. Like many pri­mates, P. thomasi may also be a host to par­a­sites such as fleas and ticks. To the ex­tent that these mon­keys serve as prey for other an­i­mals, they may im­pact preda­tor pop­u­la­tions. (Flan­nery, 2004)

• Ecosystem Impact
• disperses seeds
• pollinates

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

These lan­gurs are not known to have any par­tic­u­lar ben­e­fit to hu­mans.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Due to their pri­mary diet of fruits, leaves, and seeds, Thomas's lan­gurs are known to dis­rupt the crops of neigh­bor­ing hu­mans. ("Colobus and Leaf Mon­keys", 2001)

• Negative Impacts
• crop pest

Con­ser­va­tion Sta­tus

Due to an in­crease in the avail­abil­ity of firearms and the de­struc­tion of forests in Suma­tra, P. thomasi has to face los­ing its habi­tat and being hunted by neigh­bor­ing hu­mans. An­other fac­tor which may be re­spon­si­ble for de­clin­ing pop­u­la­tions is ha­bit­ual in­fan­ti­cide that per­sists in this species. This be­hav­ior has been known to have in­creased in re­cent years; how­ever, an in­crease in aware­ness has in­di­cated that this be­hav­ior is very im­por­tant to the species. ("Colobus and Leaf Mon­keys", 2001; "Colobus and Leaf Mon­keys", 2001; Steen­beek, et al., 1999)

• IUCN Red List

  Vulnerable
  More information

• IUCN Red List

  Vulnerable
  More information

• US Federal List

  No special status

• CITES

  Appendix II

Con­trib­u­tors

Nancy Shef­ferly (ed­i­tor), An­i­mal Di­ver­sity Web.

Matthew Wund (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Mika Matthews (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Phil Myers (ed­i­tor, in­struc­tor), Mu­seum of Zo­ol­ogy, Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

An­drom­eda Ox­ford Ltd. 2001. Colobus and Leaf Mon­keys. Pp. 380-393 in D Mac­don­ald, ed. The En­cy­clo­pe­dia of Mam­mals, Vol. II: Pri­mates and Large Her­bi­vores, 2nd Edi­tion. 132 West 31st Street, New York NY 10001: Facts on File, Inc..

Col­ijn, E., M. Muchtar. 1996. "Pri­mates of In­done­sia--Pres­bytis Thomasi (Col­let, 1893)" (On-line). The In­done­sian Na­ture Con­ser­va­tion Data­base. Ac­cessed Feb­ru­ary 08, 2004 at http://​www.​nature-conservation.​or.​id/​primates/​presbytis_​thomasi.​html.

Eimerl, S., I. De­Vore. 1965. Life Na­ture Li­brary: The Pri­mates. New York: Time-Life Books.

Flan­nery, S. 2004. "Thomas's Leaf-mon­key (Pres­bytis thomasi)" (On-line). The Pri­mata. Ac­cessed April 10, 2004 at http://​members.​tripod.​com/​uakari/​presbytis_​thomasi.​html.

Gur­maya, K. 1986. Ecol­ogy and Be­hav­ior of Pres­bytis thomasi in North­ern Suma­tra. Pri­mates, 27(2): 151-172.

Nowak, R. 1999. Pri­mates; Fam­ily CER­CO­P­ITHE­CI­DAE: Old World Mon­keys. Pp. 599-600 in Walker's Mam­mals of the World, Vol. I, 6th Edi­tion. Bal­ti­more and Lon­don: The Johns Hop­kins Uni­ver­sity Press.

Steen­beck, R., C. van Schaik. 2001. Com­pe­ti­tion and group sive in Thomas's lan­gurs (Pres­bytis thomasi): the fo­li­vore para­dox re­vis­ited. Be­hav­ioral Ecol­ogy and So­cio­bi­ol­ogy, 49(2-3): 100-110. Ac­cessed March 07, 2004 at http://​www.​springerlink.​com/​media/​gmuavwqywj238ypgdmwk/​Contributions/​X/​E/​T/​3/​XET3VU7B5K8Q97CN.​pdf.

Steen­beek, R., R. Piek, M. van Buul, J. van Hooff. 1999. Vig­i­lance in wild Thomas's lan­gurs (Pres­bytis thomasi): the im­por­tance of in­fan­ti­cide risk. Be­hav­ioral Ecol­ogy and So­cio­bi­ol­ogy, 45: 137-150. Ac­cessed Feb­ru­ary 11, 2004 at http://​www.​springerlink.​com/​media/​np330r1a8gdrrjcauq7p/​Contributions/​4/​R/​A/​U/​4RAUVQNAP5B6P0JR.​pdf.

Sterck, E. 1997. De­ter­mi­nants of fe­male dis­per­sal in Thomas Lan­gurs. Amer­i­can Jour­nal of Pri­ma­tol­ogy, 42(3): 179-198.

Sterck, E. 2002. Preda­tor sen­si­tive for­ag­ing in Thomas lan­gurs. Pp. 74-91 in L Miller, ed. Eat or be eaten: Preda­tor sen­si­tive for­ag­ing among pri­mates. Cam­bridge, UK: Cam­bridge Uni­ver­sity Press.

Swindler, D. 1998. In­tro­duc­tion to the Pri­mates. Seat­tle and Lon­don: Uni­ver­sity of Wash­ing­ton Press.