Compiled by:
Alan Varsik
General Curator
Santa Barbara Zoological Gardens
500 Ninos Dr.
Santa Barbara, California 93103
Email: avarsik@santabarbarazoo.org
Santa Barbara Zoological Gardens
Data up to August 1, 2001
CONTENTS
Introduction 3
Population Summary 5
N. leucogenys
2001 Age Pyramid 6
Census Graph 7
Births 2000-2001 8
Deaths 2000-2001 8
Living Population by Location 9
Historical Population 15
N. gabriellae
2001 Age Pyramid 26
Census Graph 27
Living Population by Location 28
Historical Population 30
Institutional List 32
INTRODUCTION
Systematics
Gibbon taxonomy continues to be a dynamic field. The number of gibbon
species varies dependent on perspective. One of the most popular
viewpoints recognizes eleven gibbon species. This studbook focuses on
members of the subgenera Nomascus, the species of gibbons formerly
considered subspecies of Hylobates concolor, they include the
white-cheeked gibbon, Nomascus leucogenys, the golden-cheeked gibbon,
N. gabriellae and the concolor or crested gibbon, N. concolor.
(Current records indicate no living black/concolor gibbons in North
America). This studbook, unlike the previous studbook, now recognizes
the genus Nomascus. This taxonomy is recognized by IUCN and has been
adopted internationally. Institutions using ARKS 4 have the ability
to generate in-house taxonomy. It is recommended that SSP
participants change taxonomy to reflect this. This will not influence
ISIS numbers. ARKS 4 can be interpreted using previous taxonomy.
Status of Wild Populations
The white-cheeked gibbon is found in the extreme southern Yunnan
(southern China) northern Laos, northern Viet Nam southwest of the
Song Bo and Song Ma rivers. The golden-checked gibbon is found in
Southern Laos, eastern Cambodia, central and southern Viet Nam.
Accurate wild populations are not known. It has been reported that
the white-cheeked/golden-cheeked group of gibbons (H. leucogenys and
H. gabriellae) appears to be the most widely distributed of the
diurnal primates in Laos. The highest calling densities have been
associated with the largest tracts of least disturbed forest in Laos.
In the two largest tracts, gibbon populations are estimated to
comprise between 400-6000 groups. Gibbons have disappeared from
smaller tracts of forest and several selectively logged and other
degraded areas.
All gibbon species are listed as endangered by the United States
Endangered Species Act and Appendix I by CITES. The Nomascus gibbons
are only found in primary or good-quality forests. They are
threatened from a variety of sources including deforestation,
poaching, and the illegal pet trade. Like many tropical forest
species the destruction of habitat has significantly reduced gibbon
populations. This is worsened by the fragmentation of suitable
habitat. The restriction or elimination of arboreal pathways that
connect gibbon populations may reduce genetic viability and further
complicate the conservation of gibbons. Increasing human populations
in gibbon habitat have created pressure to exploit gibbons in several
ways. Gibbon body parts have been sold for traditional medicines,
particularly in China. Gibbons are popular pets. As with many
animals, in order to acquire young gibbons for the pet trade, it
often includes the killing of the family group, as they will defend
their young. A monogamous social structure further threatens gibbons,
as habitat is lost. As compared to polygyny, there need to be equal
numbers of males and females in monogamous situations to maximize
population breeding potential.
Brief Ecology
Gibbons are the small arboreal apes that inhabit the tropical and
subtropical forests of Southeast Asia. They are among the most
fascinating of zoo animals; their locomotion through trees,
human-like facial expressions, song vocalization, and monogamous
family social system make them extremely popular with zoo guests.
Gibbons are classified as one of three families found in the
superfamily of apes, Hominoidea. They are the smallest of all the
living apes and belong to the family Hylobatidae and genus Hylobates.
Hylobates means "dweller in trees." They share many characteristics
with other apes, but have many qualities that are unique to gibbons.
With increasing threats to gibbons and their habitat, it is critical
that zoos continue to enlighten guests on their natural history and
utilize gibbons as a means to further an appreciation of nature and
understanding of our interdependency with it.
The Nomascus gibbons are allopatric, where their ranges do not
overlap. One of the most distinctive characteristics of the gibbons
are their vocalizations. The typical morning song bout, associated
with all gibbon species, determines and maintains the territory of
the gibbon pair or family. The songs are inflexible and seem to be
innate, not learned. This loud call can be heard clearly for great
distances and usually occurs in the darkness just prior to sunrise.
The gibbon territory would include the area needed to provide
required nutritional and reproductive resources. The vocalization not
only serves to determine the extent of the family's territory, but
also may be an indicator of their willingness to defend it. The
typical vocalization is the duet. The vocalization or 'song' of the
gibbon is also a function of the monogamous social system of gibbons.
Gibbons will defend their territory, especially to lone males that
may be in the area. Maturing juveniles will participate in the' song
'vocalization of gibbons. Gibbon duets may be comprised of separate
parts, a male and female, synchronized or similar parts that are sung
together. Variation in territory size does occur dependent on the
species of gibbon and the resources available. Territorial
vocalizations are often accompanied by physical display including
rapid brachiation in a small area and shaking of tree limbs. Except
for these territorial vocalizations, gibbons are generally quiet.
This combined with the ability to move silently through the forest
allows the gibbon to avoid predation, of which there is very little.
Gibbons are typically monogamous, a rare social system among mammals.
For gibbons, it is hypothesized that monogamy is a result of the
males' inability to monopolize more than one breeding female. This
may be due to the low density and even dispersion of females and
rigorous requirements for male parental care. Except for direct
maternal care, there is little behavioral variation between the sexes.
Gibbons are frugivores. They typically eat mostly ripe, juicy fruits
and large quantities of figs. In addition to this, they will eat
leaves, young plant shoots, flowers and, on rare occasions, birds'
eggs, birds, insects and spiders. Many zoo diets are based on
commercially produced primate chows with added fruits, vegetables and
browse. They have been known to drink by licking their own fur after
a rainstorm, dipping an arm into a tree hole or rubbing it on wet
foliage.
As in the wild, zoos typically exhibit gibbons in pairs or family
groups with infants maturing in their family group until sexual
maturity. Based on a birth interval of two to three years and the
sexual maturity of offspring, family groups can grow as large as six.
Scope of the Studbook
The studbook data is current through August 1, 2001 for both N.
leucogenys and N. gabriellae populations found in North America. The
historical population represented in this studbook is based upon
historical information that may be under the influence of different
taxonomic perspectives. The next studbook will include data through
Dec. 31, 2002 and following studbooks will be produced on an annual
basis. This studbook is available on CD-ROM and hard copy.
HOW TO OBTAIN:
To borrow this document, contact Joanne Brown
(brown@primate.wisc.edu), Head of Technical Services, Wisconsin
Primate Research Center Library and Information Service,
University of Wisconsin-Madison. Fax: 1-608-263-3512
Book received: 8-02-02
Posted date: 9-12-02
URL: http://www.primate.wisc.edu/pin/review/namgibbon.html
Page last modified:
September 12, 2002
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