Gibbons (Hylobates)
Written by: Barbara A. Sullivan
INTRODUCTION
In the early dawn hours within Southeast Asia the gibbon, a member of the lesser
apes, begins its daily vocalizations that can be heard for miles. Whether harmonizing
in duet with its mate or signifying its presence to another, the gibbon symbolizes
the delicate balance that exists between nature and man. Within the past century,
gibbon populations have declined as a result of habitat loss within the rainforest.
Land exploitation by the agricultural and logging industries, compounded by
the illegal pet trade of infant gibbons to restaurant bars and monasteries has
caused all eleven species of gibbons to declared as endangered by the USDI,
Appendix I of CITES (Nowak, 1999). One species, Hylobates concolor proves
as an excellent example of how quickly a population can be disseminated due
to human encroachment of its habitat. In 1977 the H. concolor population
was estimated to be 228,000 worldwide. In 1987 the population decreased to 131,000.
In 1983 counts were between 10,500 and 14, 000. As of today H. concolor
populations have decreased to approximately 2,500 individuals worldwide (Nowak,
1999).
Public zoos and private sanctuaries have taken on the responsibility of captive breeding programs in attempts to curtail the decreasing populations of the gibbon. Some success has been documented but many hurdles lie in waiting. Private sanctuaries are burdened with the ongoing economic challenge of providing for the daily needs of a captive gibbon. Diet, housing, medical provisions and services are only a few of the costs imposed upon a private sanctuary. Public zoos are at the mercy of government funding and thus public opinion. Political leaders once advocates of wildlife conservation, have been replaced by those who have redirected economic funding to military expansion and improvements within education. Zoos have been forced to seek funding from private individuals and/or corporations to meet their economic needs.
Gibbon survival depends on human intervention. The following information will hopefully enlighten the reader to the unique characteristics and ecological significance of this primate.
NATURAL HISTORY
Gibbons, sometimes referred to as lesser apes, belong to the taxonomic family
Hylobatidae. Within the family there is one extant genus, Hylobates
and eleven species (Chivers et al., 1978). H. lar, H. concolor,
and H. pileatus were the focus of this study.
H. lar and H. pileatus are both native to South East Asia. H. concolor inhabits Southern China, sections of Laos and Vietnam (Nowak, 1999). Phenotypes aid in identification of gibbons,due to the lack of sexual and physiological dimorphism. They range in size from 450-650 mm and weigh between 5 and 7 kg. They lack tails and have a thick pelage that varies in color (Rumbaugh, 1973). H. lar has a white-ring of fur that encircles its face. H. pileatus has a black crown on the top of its head with surrounding white fur. H. concolor has white cheek pads and a conical shaped head (Chivers et al., 1978). More recently karyotyping has aided in species identification. H. concolor has a diploid chromosome number of 52. All other species of Hylobates have a diploid number of 44 (Nowak, 1999).
Gibbons live within the deciduous and evergreen rainforests of Southeast Asia, China and Malaysia (Rumbaugh, 1974). Most of the primate's day is spent within the rainforest canopy moving about via a unique form of locomotion known as brachiation. The gibbon extends its forelimbs overhead in an alternating fashion, grasping onto branches and limbs of the rainforest canopy thus propelling itself forward in an unrestricted fashion. Brachiation allows the gibbon to forage within a large territory/home range during the changing seasons. Fruits and plants constitute approximately 75% of the gibbon diet (Kirkwood et al., 1992). Gibbons aid in seed dispersal within the rainforest as it moves about its territory, expelling undigested seeds in its feces. When fruits and plants are in short supply the gibbon will feed upon spiders, ants, termites, grasshopper and other rainforest invertebrates ( Kirkwood et al., 1992). The gibbon obtains water by placing the back of its hand and fingers onto the surface of leaves and other foliage where condensation has collected. The gibbon then proceeds to suck the water from the fur of its hand and fingers (Roonwal et al., 1997) and (Personal observation, June 2001).
Within its home range (an area in which the gibbon inhabits but does not always defend) the gibbon will provide food for its young and other family members. Gibbons are thought to be monogamous, although recent studies have documented individuals who have sexually viable mates, to copulate with other gibbons in the wild (Fuentes, 2000). Environmental stresses such as depleting food supplies, has been hypothesized to threaten the gibbon's genetic fitness and thus instigate behavior that would ensure reproductive success such as multiple mates (Fuentes, 2000). The traditional family unit has been documented as one adult male, one adult female and two to three young at different developmental stages. They range from infant (birth to 1.5-2 years), juvenile (2- 4.5/5 years), sub-adult (4-6/7 years) and adult (6/7 years) at which time both male and female reach sexual maturity. Gibbons appear to lack a seasonal breeding period with births occurring throughout the year (Rumbaugh, 1975) and (Kirkwood et al., 1992). Once mated the female undergoes a gestation that lasts between 190-214 days (Kirkwood et al., 1992). Young are born every two to three years and will remain with the mother until approximately 5-6 years of age. The sub-adult will then be cast out and forced to survive independent of its family (Kirkwood et al., 1992). This usually proceeds the weaning of an infant that will allow the female to care for a new infant soon to be born (Roonwal et al., 1997). Litter size is usually one with the young capable of sight at birth. Within hours the newborn in able to cling ventrally to its mother by which it will spend most of its first year (Kirkwood et al., 1992). Mating poses a grave danger to the growing infant. Sexually active males have been documented to aggressively bite an infant's arm in attempts to mate with the female. In the wild this can cause death due to severe blood lose. Young captive gibbons, which have been the target of such male aggression, will have had partial or complete arm amputations that were necessary to stop blood lose and thus ensure survival (Personal communication with Pharanee Deters, June 2001). Both male and female have a "reproductive life span" of 10-20 years (Kirkwood et al., 1992). Gibbons have been documented to live in captivity up to 45 years with wild populations showing a greatly reduced lifespan (Rumbaugh 1973), (Roonwal et al., 1997) and (Personal communication with Pharanee Deters, October 2001).
EVOLUTION
The first known fossil records of gibbons are those of jaw and teeth fragments
found in Africa (Nowak, 1999). They date back to the Oligocene epoch. It is
at this time that Hylobatidae is believed to have evolved from their
ancestor the cattarrhines (old world anthropoids), as did the Pongidae (the
great apes) that would eventually give rise to the Hominidae, Homo sapiens
(Jablonski et al., 2000). During the Miocene and Pliocene epochs, fossils documenting
the presence of Hylobates have been located in Africa, Europe and Asia (Nowak,
1999). Currently the most definitive gibbon fossil was found in the Szechaun
Province of China, dating back to the middle Pleistocene epoch. A jaw with intact
molars 1 and 3 resembled the current molariform dentition of the modern gibbon
(Rumbaugh, 1973). Eastern Asia at this time was undergoing extreme climate changes.
In the early Pleistocene the tropical zones of the Himalayas and the Plateau
of Tibet inhabited by Hylobates, began a longitudinal constriction that
would continue into the late Pleistocene (Jablonski et al., 2000). During this
time the gibbon was forced to migrate south into subtropical rainforests (25
degrees north latitude) where foodstuffs were seasonal. Brachiation would provide
a means of locomotion by which seasonal fruit and plants could be obtained with
a minimum of energy loss over very large distances (Jablonski et al., 2000).
Hylobates radiation
appears to have peaked during the late Pleistocene as gibbons recolonized within
various subtropical environments of Southeast Asia. Physical isolation due to
environmental and geographical changes, (ie., the increasing sea levels over
the Sundra Shelf) is believed to have prompted species' specific adaptations
that would ensure reproductive success (Jablonski et al., 2000).
THE ANATOMY OF BRACHIATION ( A BRIEF
STUDY)
Brachiation, key to survival for the gibbon, has been made possible by several
unique morphological adaptations of the muscular and skeletal systems. Increased
shoulder mobility is possible via highly developed muscles of the rotator cuff.
The levator clavicular, subscapularis, supra and infraspinatus, and teres minor
work in conjunction to hold the humerus within the glenoid cavity thus reducing
the chance of dislocation (Rumbaugh, 1975). A synergy between well developed
muscle tissue and insertions deep within even stronger adjacent muscles (i.e.,
the levator clavicular inserts deep into the trapezius), provides a network
that will allow for increased shoulder rotation while providing joint stabalizaton
(Rumbaugh, 1975) and (Rumbaugh, 1973). The scapula and clavicle, onto which
the trapezius and serratus anterior insert, are higher and more dorsally located
than in many other primates thus enhancing shoulder rotation (Rumbaugh, 1975).
The forearm and wrist also provide anatomical adaptations necessary for brachiation. The pronators and supinators of the forearm are elongated and well developed, allowing the radius to rotate around the ulna without experiencing muscle fatigue (Rumbaugh, 1975) and (Jenkins, 1981). The Hylobates wrist is quite unique in that it has a ball and socket joint allowing for biaxial movement. Compare the human wrist, which comprises a plane joint that allows for only gliding movements on a nonaxial plane (Jenkins, 1981) and (Marieb et al., 1997). When a gibbon grips a tree limb during brachiation the distal metacarpal bones, phalanges and the palm of the hand remain on one plane while the proximal metacarpals and forearm can rotate up to 180 degrees around the vertical axis of its outstretched arm (Chang et al., 2000). The extensors and flexors of the forearm provide the necessary strength during rotation, thus eliminating any stress that might have been imposed upon the shoulder joint (Jenkins, 1981). This unique midcarpal joint of the wrist allows the gibbon to grip onto limbs with increased accuracy, while propelling itself forward at various speeds and levels within the forest canopy. The ball and socket joint in conjunction with the muscular strength of the forearm reduce energy expenditure via decreased resistance of rotation around an axis (Chang et al., 2000) and (Jenkins, 1981). Compare a gibbon crossing a set of monkey bars with that of a human. The human would be unable to rotate his/her wrist to a 180-degree angle while gripping the above bar during locomotion. Most of the rotation would originate at the shoulder joint and thus generate huge energy demands upon the surrounding muscles of the upper arm and torso. Gibbons are not hindered by such energy constraints and forage throughout the day over large areas within their territory.
GIBBON CONSERVATION
All eleven species of gibbons are in grave danger of extinction. The destruction
of the rainforests and illegal poaching has caused populations to decline at
an exponential rate. Zoos and private sanctuaries are attempting to curtail
the gibbon decline in Southeast Asia via captive breeding programs. Those who
attempt to aid in gibbon conservation are consistently plagued with many cultural
and economic barriers. Pharanee and Bill Deters, owners of the Highland Farm
in the Tak province of Thailand, have been involved with the plight of the gibbon
since 1991. A hunter who had killed its parents for their meat brought the first
gibbon to the farm. Ten years later the Deters' now provide homes for 35 gibbons.
Three gibbon species are represented at the Highland Farm: Hylobates lar,
Hylobates concolor, and Hylobates pileatus. Each gibbon has a
unique history that can stem from birth in the wild, to abuse/neglect by previous
owners, or simply the inability of a human caregiver to safely cohabitate with
a sexually mature gibbon. After all is said and done, every gibbon arrives with
its own set of baggage, thus posing many challenges to a captive breeding program.
ABNORMAL BEHAVIOR OF CAPTIVE GIBBONS
Many adult captive gibbons show signs of abnormal behavior as a result of losing
maternal contact within the first two years of life. If early contact is limited
to humans, erroneous imprinting may lead to fear, aggression and/or lack of
sexual interest towards conspecifics in an adult gibbon (Mootnick et al., 1994).
The behavior of masturbation among captive gibbons was the focus of a study
conducted by Alan Mootnick and Elaine Baker at the International Center for
Gibbon Studies in Santa Clarita California. David, a male H. concolor,
at Highland Farm was observed to engage in such behavior. Little history is
known of David other than he was acquired form the Dusit Zoo in Bangkok, Thailand
by the Deters in December of 1999. His right forearm was severely mutilated
after being bitten by another gibbon while housed within a zoo enclosure. The
forearm was amputated in an attempt to ensure David's survival. As one approaches
David's enclosure at the Highland Farm he will sit upon an elevated branch while
masturbating, all the time watching his captive human audience. Some have proposed
that masturbation can be a result of early isolation from the mother and other
conspecifics if it occurs before two years of age (Mootnick et al., 1994; Mootnick
et al., 1997). Self-stimulation in conjunction with early social contact that
is limited to humans, conditions the young gibbon to relate to the human as
a conspecific. When reaching adulthood, sexual interest in other gibbons is
often absent and can result in sexual inadequacy (Mootnick et al., 1994). Though
a major hurdle to captive breeding programs, the negative behavior of early
maternal isolation can be reduced if not eliminated by socialization from other
young and sexually inexperienced conspecifics (Mootnick et al., 1997). Sexual
behavior is presently believed to be more a result of bodily contact and subsequent
responsiveness than of imitating adult behavior, as seen in other primates (Mootnick
et al., 1997). As a young gibbon matures in the presence of other conspecifics
of the same age, behavior that reinforces sexual stimulation is learned through
contact play and other social interactions (Mootnick et al., 1997; Rumbaaugh,
1974).
Highland Farm currently has four juvenile gibbons housed in one enclosure. They are frequently involved in a game of chase and tag that is often abruptly interrupted by the approach of a visitor to their enclosure. The juveniles are curious and rambunctious. They show no signs of relating to the visitors as conspecifics. The presence of humans appears to provide a brief digression from their everyday routine. Such behavior towards other gibbons in the future will hopefully ensure sexual proficiency and thus lead to a more productive breeding program.
Unfortunately, all abnormal behaviors cannot be reversed. Denise, a female H. lar, came to Highland Farm in June of 1998. Pharanee Deters had discovered her in a Buddhist monastery where she was continuously housed within a 3X2X2 cage. After several visits, and with the tenacity of a mythical Greek goddess, Ms. Deters acquired Denise and brought her to Highland Farm. Emaciated and suffering from self-inflicted alopecia, the Deters began an intensive recovery program that emphasized proper nutrition, adequate housing and human interaction. Over time Denise gained weight and regrew the fur she had lost. While in recovery it was noted that Denise would periodically pull out her own hair and ingest it. Such behavior has been documented in other animals that have been exposed to very high and reoccurring levels of stress. Prior experience with the rehabilitation of young abused gibbons has taught the Deters that intensive medical care and human interaction should continue for a six month duration for successful introduction to another conspecific. Young gibbons can show signs of fear and aggression if subject to environments that appear hostile or theatening due to premature introduction.
As Denise's recovery continued the Deters' introduced her to a male H. lar, Max. Self taught in animal husbandry, the Deters and their farm laborers constructed a cage that would properly house the two adult gibbons. As recently as June of 2001 they continue to share the enclosure. Denise and Max are often viewed grooming each other. Such behavior is believed to reinforce a vital social bond necessary if the two are to some day mate and produce an offspring. Currently Denise has been viewed to display behavior that would suggest a sexual interest in Max. Unfortunately, she continues to self-groom causing regions of alopecia on her forearms and legs. The slightest stressor (i.e., a new volunteer or farm laborer) can instigate this conditioned response that had been reinforced during her early years of confinement. Although somewhat shy, Denise displays little fear of humans, allowing a visitor to rub her extended arm for short durations. Such trust is the result of many hours that were dedicated by the Deters in hopes of healing Denise's physical and emotional wounds.
PHYSICAL DEFORMITIES OF A CAPTIVE
GIBBONS DUE TO IMPROPER HOUSING
Another gibbon of special interest was George, a male H. lar. He came
to Highland Farm when approximately three years old. A representative from WAR
(The Wild Animal Rescue Foundation of Thailand) inquired if placement with the
Deters at Highland Farm would be possible for this very affectionate and gentle
gibbon. George would have special needs due to the physical deformities that
resulted from being housed in a very small birdcage prior to reaching WAR. The
inadequate space impeded muscular activity that eventually lead to severe and
irreversible muscle atrophy of the right side of his body. George lost all use
of his right arm and partial use of his right leg. The Deters agreed to take
responsibility for George and promptly returned to Highland Farm. Proper housing
and nutrition were immediately implemented. Bill often reminisces of the long
hours Pharanee spent sitting next to George in his temporary quarantine cage
while speaking softly to her newfound friend. Eventually, George would extend
his arm through the bars of the cage awaiting Pharanee's gentle touch. This
was a milestone; such socialization/trust would allow the Deters to introduce
George into a new and permanent enclosure with a minimum of stress. Due to his
physical limitations George lives alone within his enclosure. Both female and
male gibbons have been documented to attack potential mates. George would have
no means of defending himself, possibly sustaining life-threatening injuries.
He is capable of brachiating to various levels within the enclosure and maintains
a playful and curious disposition.
ENCLOSURES FOR CAPTIVE GIBBONS
Many of the visitors to Highland Farm gaze with amazement while watching the
gibbons brachiate. Although capable of walking in an upright position, Hylobates
has evolved to occupy a niche within the rainforests that is possible via brachiation.
Proper housing for captive gibbons should simulate the various elevations of
the rainforest canopy, with a minimum of two vertical levels. The enclosure
should also measure at least six arm lengths wide by two arm lengths deep, increasing
by one arm length in width for each additional gibbon (Mootnick et al., 1997).
This allows all animals sharing an enclosure to brachiate simultaneously as
they would if living in the wild. Such an environment reduces the stress of
captivity and allows for proper socialization between a potential mating pair
(Mootnick et al., 1997).
THE CULTURE AND ECONOMY OF THAILAND:
THE CHALLENGES THEY POSE TO HIGHLAND FARM
Highland Farm is located in a very culturally diverse region of Thailand. Many
of the inhabitants from the surrounding farms include those who belong to the
various Hill Tribes: immigrants from adjacent countries that have relocated
for a multitude of reasons. From The Socialist Republic Union of Myanmar, formerly
Burma, are the Karin, Arkar and Lisu. All have inhabited this region for sometime
and are known to have hunted wild gibbons for their meat. The Humong and Yunan
are of Chinese origin. They do not condone the slaughter of gibbons due to religious
convictions. Hill Tribe members are primarily agricultural workers farming crops
of rice, potatoes, cabbage, lettuce and other vegetables. Many live in housing
void of running water and electricity. Their days are long and hard, often working
months at a time without a day's rest. Such a lifestyle usually does not lend
itself to embrace the plight of the gibbon. The Deters long ago recognized the
need to educate others of the gibbons' fight for survival and opened the sanctuary
to all, free of charge. This ideology continues today even with the financial
constraints of a private sanctuary.
Highland Farm continues to provide many visitors with the rare opportunity to watch, hear and study three species of Hylobates. Vocalizations can be heard from the early morning hours of 5:00 a.m. into midafternoon. Whether claiming territory or dueting with a potential mate, the song of the gibbon is impossible to ignore. Ms. Deters is often approached by visitors to the sanctuary, that share tales of a time in the past when wild gibbons could be heard in the rainforests that used to comprise most of the Tek Province.
THE ROSE INDUSTRY AND THE ILLEGAL
CHEMICALS THAT KILL
Located in the eastern fringe of the Phop Phra district of the Tek province,
Highland Farm is within what has been labeled as one Thailand's "biggest
chemical dumpsites" (Tripathi, 2001). The rose industry is huge and continues
to grow within this region, due to demand from cities such as Bangkok and Chiang
Mia.
Roses are very susceptible to the damaging effects of insect infestation. In attempts to curtail the economic loss of crop damage, rose farmers treat their fields with insecticides that have been deemed illegal by the government of Thailand. The adjacent land to the Deters' property is a rose farm that uses such illegal insecticides. Labels confiscated from trash bins within the rose farmer's property confirmed such illegal practices. The above photos are of bottles that contained the organophosphate dimethyl (E)-1-methyl-2-(methylcarbomoyl) vinyl phosphate or more commonly known as Monocrotophos. The insecticide is produced and distributed by Phato Chemical Industries in Bangkok, Thailand. The labels were dated December 4, 2000 by the manufacturer confirming recent production and distribution. Currently no registrations for monocrotophos exist in the United States. Due to the high level of toxicity that could be spread via respiratory route or dermal exposure most applications within the United States were deemed illegal in the late1980s with a few exceptions that were alleviated by the spring of 1999 (Personal communication with Amy Mysz October, 2001).
Organophosphates, carbamates, organochlorines, pyrethroids, thiocarbamates, and paraquats are used to eliminate insect populations. In primates they have been proven to affect the CNS and respiratory systems, causing neurological damage and possible respiratory arrest. Field workers of the adjacent rose farm were observed spraying such toxic chemicals without proper protection and without regard to weather conditions. It was not uncommon to see the insecticide aerosols pushed by the winds into the fields and houses of Highland Farm. The gibbons would innocently sit within their cages, inhaling the harmful toxins.
The Deters' have little recourse to such blatant disregard for human and animal life. The local government and regional rose farmers negate their responsibility to uphold and abide by the laws imposed by the government of Thailand which has declared such chemical use to be illegal. Organophosphates are known to be endocrine disruptors and are currently believed to play a major role in reduced male sperm production, thus posing one more problem to Highland Farm's captive breeding program.
Gibbon conservation faces many challenges in the years to come. The Deters believe that wild gibbon populations are decreasing at such an extreme rate, that private sanctuaries and zoos will be the only place to view a live gibbon in the future. If this is to become the fate of the gibbon, funding must exceed what is currently be generated. Food, housing and medical provisions are necessities that are rarely donated and yet comprise the essential basics for survival of the gibbon.
Websites with information of gibbon conservation
have been provided as follows:
The Highland Farm: http://highlandfarm.tripod.com/gibbon/gibbon.htm
International Center for Gibbon Studies in Santa Clarita, California: http://www.gibboncenter.org
WAR: http://www.warthai.org/
ACKNOWLEDGEMENTS
The author wishes to express her gratitude to the following:
Pharanee and Bill Deters with whom this research would not have been possible.
Dr. Robert Howe whose faith in my capabilities often surpassed my own.
Dr. Donna Rich who without hesitation approached the very complicated subject of gibbon anatomy with fortitude and grace.
Dr. Ronald Starkey whose knowledge of organic chemicals and their structure combined with a genuine sense of humor turned what could have been an intimidating topic into one of exploration.
Dr. Robert Bickner whose translation of the Thai language aided in my efforts to inform others of the illegal insecticide used within the rose industry of Thailand.
Amy Mysz of the U.S.E.P.A. Her prompt and detailed response to my questions of monocrotophos use in the United States was far beyond my expectations.
Nick Marto, Gwen Davis, Chad Joubert, and Andy Speth of The University of Wisconsin, Green Bay Learning Technology Center.
Dr. Deborah Swackhamer of the University of Minnesota. Her help with the many references and the information they provide allowed me to collect data by which further research was obtained in a very timely manner.
Dr. Robert Olsen whose wisdom and teachings of the human soul provided me with the strength to look within my own, and not only see the truth but write of it.
As always, to my husband Michael, whose unconditional support in my quest for knowledge continues to leave me in awe.
Last, but not at all least, I am indebted to the farm laborers of Highland Farm. Their warm smiles reflected their inner strength that I so learned to respect.
Kob Khun
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The Nation.
A newspaper written and distributed in Thailand.
Reproduced here courtesy of Barbara Sullivan ©
