Geographic Range
The entire population of the Hainan black-crested gibbon,
Nomascus hainanus
, is found in the 300 km^2 Bawangling National Nature Reserve (BNNR) on Hainan Island
off of the coast of China. Historically,
N. hainanus
was widespread on Hainan Island but a recent estimate put its entire geographic range
as low as 14 to 16 km^2 of BNNR.
- Other Geographic Terms
- island endemic
Habitat
Hainan black-crested gibbons live in tropical primary forests. It is estimated that
95% of their original habitat has been lost. Hainan black-crested gibbons require
indigenous forest of Hainan Island and do not inhabit recently planted pine forests
or rubber plantations. Due to habitat loss and hunting, this species has shifted its
primary habitat from lowland forest to higher mountainous forest (with elevations
ranging from 100 to 1800 m on Hainan Island). Optimal habitat is hard to determine
as a result of the small population size and altered environment on the entire island.
However, mature, ravine tropical forests, in particular, seem to be favored. Like
other gibbons, Hainan black-crested gibbons are specialized for living in the canopies
of forests.
- Habitat Regions
- tropical
- terrestrial
- Terrestrial Biomes
- rainforest
- mountains
Physical Description
Adult males and juveniles have completely black pelage while females are brownish
buff with some black hairs appearing on the limbs as they age. Males and females have
a large black crest of fur on the top of their heads. The crest is approximately 10
by 3 cm. Females also have a characteristic white face ring. Infants are born tawny
brown, becoming black within 5 to 6 months.
Adults weigh between 5.8 and 10 kg. Hind limbs are 70.4% the length of forelimbs,
which is slightly longer than in other black-crested gibbons (
Nomascus
species). The interorbital distance ranges from 10.4 to 10.7 mm. Along with pelage
coloration, physical size is the main identifying characteristic of
Nomascus
species. Due to the rarity of Hainan black-crested gibbons, very few specimens have
been collected and little is known of variation in size. However, within gibbons there
is little variation in body size. Most likely
N. hainanus
has a similar body length as other gibbons and this assumption is supported by anecdotal
evidence (Pocock 1905). Lar gibbons (
Hylobates lar
) are reported to reach an adult size of 42 to 60 cm in length (excluding the tail).
There is no sexual dimorphism in size in gibbons. However, there is sexual dimorphism
in coloration, also known as sexual dichromatism.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes colored or patterned differently
Reproduction
Social polygyny, with two females and a single male, is the usual mating system in
N. hainanus
. Females initiate mating by approaching a male and moving their head and limbs in
rhythmic, jerky motions. Multiple copulations via dorsoventral mounting may occur
in a single day. Sexually active females occasionally engage in post-conception copulation,
which is relatively rare amongst the primates.
- Mating System
- polygynous
The amount of time between births is approximately 24 months. This timing may be caused
by biannual fruiting of many favored food sources and thus link reproduction with
the abundance of food. Two females in a single social group may rear offspring from
the same male at the same time. Gestation has been estimated to be 136 to 173 days.
- Key Reproductive Features
- iteroparous
- gonochoric/gonochoristic/dioecious (sexes separate)
- sexual
- viviparous
Infants are dependent on their mother for the first 1.5 years of their lives, but
remain in the social group as juveniles for some time after this. It is during this
infant dependency period where lactation occurs. Lactation is energetically costly
for female
gibbons
of other species.
In one case, a maturing male offspring was driven out of the group at 5.5 years of
age. This is quite early compared to most other gibbon species, which mature from
6 to 9 years. A possible reason for this eviction, besides actual sexual maturity
is that, due to limited resources, the alpha male may have been forced to drive out
the maturing offspring.
- Parental Investment
- female parental care
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
Although lifespan data is limited due to their rarity,
gibbons
live longer than most other primates, with a record of 60 years in a
Hylobates muelleri
individual. Lifespan is not reported in
Nomascus hainanus
.
Behavior
Hainan black-crested gibbons are found in social groups composed of females, juveniles,
infants and, occasionally, males. Males will also live solitarily. Group size has
been hard to determine due to the extremely low population size and fluctuations in
behavior of
N. hainanus
as a result of the degradation of habitat.
The most common form of locomotion in a closely related species of black crested gibbon
(
Nomascus concolor concolor
) is brachiation (rapid swinging from branch to branch via the forelimbs) through
the canopy. Leaping, walking and climbing were also observed but the gibbons were
never seen to come to the ground. Brachiation has also been observed in
N. hainanus
.
Home Range
Nomascus hainanus
individuals occupy home ranges of 200 to 500 hectares (2 to 5 km^2), which are the
largest home range sizes of any gibbon. However, this large size might be the result
of reduced intraspecific competition or increased area between suitable food patches.
It is suggested that home range size might recently have increased to nearly 1000
hectares (10 km^2) due to degradation of habitat quality.
Communication and Perception
Hainan black-crested gibbons often perform morning duets between male and female pairs.
The female usually only emits a single loud noise often referred to as a great-call.
The male’s song is more elaborate and has at least three distinct calls. The presence
of a laryngeal sac in males may contribute to the increased complexity of vocalizations.
Hainan black-crested gibbons are believed to be the only gibbon species with a male
dominated duet.
Hainan black-crested gibbons are one of only three gibbon species in which the female
makes vocalizations during mating. There are many hypotheses concerning these soft
grunts of the female but it might have be related to the social polygyny of
N. hainanus
and it may be an advertisement of ovulation to other females.
- Other Communication Modes
- duets
Food Habits
Hainan black-crested gibbons are almost exclusively frugivores. In the refuge they
inhabit, the most common food sources are the fruits from
Litchi canensis
,
Nephelium topengii
, and various
Ficus
species.
Figs
in particular have been noted as a favored food source. Closely related species of
gibbons eat insects, seeds, and grains and
N. hainanus
may have a similar diet.
- Animal Foods
- insects
- Plant Foods
- leaves
- seeds, grains, and nuts
- fruit
Predation
Tree selection for sleeping is an antipredator behavior for gibbons. They often sleep
in the tallest trees in an area which would safeguard them from most terrestrial predators.
Gibbons also sleep on branches with many twigs so that the twigs, which vibrate easily,
will act as an early warning system. Hainan black-crested gibbons were not explicitly
mentioned in a Fei et al. 2012 study, but these insights into their close relatives,
N. nasutus
, may hold true for them as well.
Two attacks from an unidentified species of hawk lasting approximately 15 minutes
have been observed on
N. hainanus
. A species survey of Hainan Island recorded 7 species of carnivorous eagles and hawks.
Humans are the main predators of Hainan black-crested gibbons. Humans can benefit
by selling adults into the illegal animal trade, use the meat for food, or sell the
bones for use in traditional Chinese medicine. Mass slaughters have been recorded
on numerous occasions.
Ecosystem Roles
Hainan black-crested gibbons have been described as an umbrella species for the local
ecosystem. An umbrella species is one which indicates the overall health of an ecosystem.
Gibbons may also play a role in the seed dispersal of many of the fruits that they
eat.
- Ecosystem Impact
- disperses seeds
Economic Importance for Humans: Positive
Hainan black-crested gibbons can act as seed dispersers for forest tree species. Trade
in live
N. hainanus
as well as body parts, can result in hefty profits from black market Chinese medicine.
There is no proven efficacy of these traditional "medicines" and the impact on wildlife
populations is devastating.
- Positive Impacts
- source of medicine or drug
Economic Importance for Humans: Negative
Due to the critically endangered status of Hainan black-crested gibbons, the Chinese
government has put a ban on all types of forestry in or around BNNR. Hainan Island,
which is home to many introduced rubber plantations, has been forced to stop the expansion
of the rubber industry in order to save
N. hainanus
and other endangered species. This is a short-term negative economic impact, but
has long-term positive impacts because it helps to protect a critical and unique ecosystem.
Conservation Status
The IUCN currently lists Hainan black-crested gibbons as critically endangered. Some
have suggested that they are the rarest mammals in the world, with approximately 20
individuals counted in a recent survey. A major concern is that of the approximately
20 individuals left, only 4 are adult females and one of these may be post-reproductive.
Numbers have increased since 2003, when it was believed that there were as few as
13 individuals.
Conservation efforts are varied. Technologies such as remote sensing and geographic
information systems are being used to determine suitable habitats. The government
is also planning on adding to the list of protected forest on Hainan Island. In 2003,
the Hainan Gibbon Action Plan was launched. Population surveys, reforestation, and
the training of staff to monitor the gibbons are all parts of the Action Plan.
Habitat loss and human encroachment and activity are the main reasons for the decline
in population of Hainan black-crested gibbons. The species has seen a drastic reduction
in range and population since the 1950s. The annual rate of habitat loss is approaching
zero, although more work needs to be done concerning critical habitat conservation,
but Hainan black-crested gibbons are, without a doubt, on the very edge of extinction.
Other Comments
It is important to note that
N. hainanus
and most other
gibbon
species are in the midst of controversy concerning their classification. By the 1980s,
Ma et al. reported that
N. hainanus
has been known as
Hylobates hainanus
,
Hylobates pileatus
,
Hylobates concolor concolor
and was then known as
Hylobates concolor hainanus
. Wei et al. noted that since the 1980s the species has been known as
Nomascus concolor
,
Nomascus nasutus
, and
Hylobates
(
Nomascus
)
hainanus
. Wei et al referred to the species as
Nomascus
sp. cf.
Nasutus hainanus
. The species is now known as
Nomascus hainanus
based on morphological, vocal, and genetic characters.
There are currently four genera of gibbons;
Hoolock
,
Hylobates
,
Nomascus
, and
Symphalangus
. Each genus differs in the number of chromosomes, with all six species of
Nomascus
having 52. Zihlman et al. believe that the distribution of body mass can also be
used to classify species into these genera.
Additional Links
Contributors
Rob Gregoire (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.
- oriental
-
found in the oriental region of the world. In other words, India and southeast Asia.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- island endemic
-
animals that live only on an island or set of islands.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- terrestrial
-
Living on the ground.
- rainforest
-
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
- mountains
-
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
- endothermic
-
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- polygynous
-
having more than one female as a mate at one time
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- female parental care
-
parental care is carried out by females
- arboreal
-
Referring to an animal that lives in trees; tree-climbing.
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- social
-
associates with others of its species; forms social groups.
- visual
-
uses sight to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- duets
-
to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- chemical
-
uses smells or other chemicals to communicate
- drug
-
a substance used for the diagnosis, cure, mitigation, treatment, or prevention of disease
- herbivore
-
An animal that eats mainly plants or parts of plants.
- frugivore
-
an animal that mainly eats fruit
References
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