Comments On: For ET
From: Brad on 03/25/98
Primate Gallery's Primate of the Week Whitehanded or Lar Gibbon note 1of 2 For ET
Gibbons are the smallest of the apes. Most species weigh about 5 kg, although Hylobates hoolock weigh slightly more (6 to 8 kg), and the siamane Hylobates syndactylus is twice as large (10 to 12 kg). Gibbons are prototypical brachiators, with long arms and hands and flexible forelimb joints. Scientists are still debating whether these morphological features originally evolved for efficient food collection (i.e. hang-feeding and climbing on small branches;) or for efficient travel between food sources. The small size and suspensor locomotion of gibbons permit them to move more easily and directly through the rain forest canopy than sympatric orangutans and macaques.
Geographic Range: Gibbons are restricted to tropical evergreen and less seasonal parts of semievergreen rain forests in Asia. H. agilis occur in Sumatra, West Malaysia, southwestern Borneo, and southern Thailand; concolor in Vietnam, Laos, Cambodia, and southern China; hoolock in Asam, Bangladesh, and Burman; klossii in the Mentawai Islands west of Sumatra; lar in Thailand, peninsular Malaysia, and northern Sumatra; moloch in western Java; muelleri in all of Borneo but the southwestern corner; pileatus in southeastern Thailand and western Cambodia; and syndactylus in Sumatra and peninsular Malaysia. The siamang is sympatric with lar and agilis. All other species are allopatric, except for slight overlap between lar and pileatus in Thailand, between lar and agilis in West Malaysia, and between agilis and muelleri in Borneo.
Natural History: Gibbons are frugivores. They eat mostly ripe, sugar-rich, juicy fruits and also large quantities of figs (Ficus fruits). Fruit comprises about 60% and leaves 30% of the diet for most of the smaller gibbons, but monthly proportions of fruit sometimes exceed 90% or fall below 30%. The larger siamang (H. syndactylus) is more folivorous, klossi and pileatus may be more frugivorous, and klossii apparently obtains protein primarily from insects instead of young leaves. Gibbons have fixed home ranges that average about 34 hectares, (85.614 acres) with exclusive portions (territories) averaging 75% of this area. Siamang home ranges are smaller than those of sympatric lar groups, but similar in size to those of many other gibbon species. Gibbons are active from 8 to 10 hours a day on average. Activity usually starts at dawn and stops well before sunset. Adult males and offspring become active sooner and often stay active later than females. Singing and the most intense feeding occurs in the morning, but compared to most other primates, gibbons show little change in activity over the day. Gibbons spend most of their day foraging in the main canopy (ca. 20 to 35 m high in primary forest). Emergent trees are used primarily to rest, sleep, and sing. Little time is spent in the lower canopy, and this mostly to visit small food trees.
Reproduction: Male and female gibbons mature at similar rates and appear to pair at 8 to 10 years of age. Females first menstruate at around 8 years of age. Brad and Trouble
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From: Brad on 03/25/98
Primate Gallery's Primate of the Week Whitehanded or Lar Gibbon note 2 0F2 For ET
They do not have sexual swellings; however, Carpenter and Chivers both describe changes, presumably associated with ovulation, in the color and turgidity of female genitalia. Females cycle for only a few months (ca. 5), at intervals of 2 or more years between births, and copulations during these periods of sexual activity occur at a rate of less than once a day.
Social Organization: Gibbons are invaribly monogamous and territorial, and defend their territories through regular loud morning songs and occasional encounters with neighbors and intruders. Outside these intergroup activities, gibbon families lead a relatively subdued social life. In addition to the adult pair, a gibbon group potentially includes one infant (0to 2 or 2.5 yr), one juvenile (2 to 4 yr; defined by locomotion independent of the mother), one adolescent (4 to 6 yr; not yet adult sized), and one subadult (6+ yr; fully grown, but unmated). Mean group size is usually about four. A mated pair produces an average of five to six offspring over a reproductive lifetime of 10 to 20 years. No stable groups have been observed with more than one female carrying an infant. Female gibbons weigh nearly the same as males and have similar-sized canines. H. concolor, hoolock, and pileatus have sexually dimorphic coat colors, and all species but hoolock have sexually dimorphic vocal repertoires. Males and females without sex-specific coloration are hard to distinguish by sight if the female is not carring an infant or if, as is often the case, the observer cannot get a close and clear enough view to spot enlarged nipples or parapenal hair tufts. Sexual monomorphism in gibbons is correlated with a comparatively high degree of behavioral and social equality between adult males and females. Partners in long established pairs normally interact in a relaxed, tolerant, and well-coordinated manner. In contrast to many species of primates, female gibbons are often "codominant"with males.
Conservation Status: Hylobates lar: CITES - Appendix I; U.S. ESA - Endangered. Gibbon populations are currently threatened most by loss of habitat to cultivation and commercial logging. Gibbon densities may decline minimally and temporarily where few trees are extracted from a forest, but in most timber operations, logging is intensive and appears to increase forest destruction caused by agricultural encroachment, flooding, wind starms, and forest fires. Their future depends on the maintenance of the forest reserves to which they are not primarily or entirely restricted. Brad and Trouble
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From: Glen Knowles on 10/04/99I teach animal drawing at the Los Angeles Zoo. I am attempting to discover what the average height and arm span of Gibbons are. Or that of a specific individual. Every source I bring up just says they have really long arms. I need more accurate information than casual observation for a hand-out for my students!
Thanks
Glen
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