SOCIAL ORGANIZATION AND BEHAVIOR
Lar gibbons usually live in serial monogamous pairs with up to 4
offspring in each group (Palombit 1996; Bartlett 2007; Reichard 2003;
Reichard & Barelli
2008). While group living in serial monogamous pairs is the norm, it is not the rule,
and at some sites there are also multi-male groups as well as groups with
multiple adult females (Reichard 2003; Barelli et al. 2008b; Reichard &
Barelli 2008). Long-term data indicate that females may live in several
different types of groups (e.g. pair or multi-male) over their lifetimes
(Reichard & Barelli 2008). At one location, multi-male groups comprised
over 20% of groups present (Reichard & Barelli 2008). Extra-pair
copulations have been seen on a number of occasions (Reichard 1995; Reichard
& Sommer 1997; Reichard 2003). In fact, at Khao Yai, most females are
polyandrous as opposed to monogamous, even females in a single-male group
(Barelli et al. 2008b; Reichard & Barelli 2008). In other words, social
relationships are flexible (Reichard 1995; Reichard & Barelli 2008). In the
case of individual pair-bonds, changes can result from desertion (often for
another mate), replacement of one of a pair by a peripheral individual,
disappearance or the death of one of the adult lar gibbons (Palombit 1994;
Brockelman et al. 1998). Changes in pair composition can be common (Palombit
Within-group behavior is variable throughout the year, from almost a
fifth of the activity budget to only a small percentage, with more social
activity occurring at times of increased ripe fruit abundance. The three
predominant types of within-group social interaction include grooming, play
(wrestling, chasing, and slapping and biting), and social contact, with grooming
the most common. Within-group aggression is rare and in general, immature lar
gibbons play more than adults (Bartlett 2003). There are some indications that
allogrooming serves more a hygienic than social function in lar gibbons and
tends to be reciprocal between individuals (Ellefson 1974; Reichard & Sommer
Encounters between different groups of lar gibbons can range between
agonistic (physical altercations) and friendly (between-group playing or
grooming) interactions (Reichard & Sommer 1997; Bartlett 2003). Most
interactions between groups are agonistic, but can be purely vocal and even
neutral in which both groups coming into contact barely react to one another
(Bartlett 2003). Groups may also travel, feed or rest together when they come
into contact (Reichard & Sommer 1997).
Males mainly participate in most territorial disputes, but females
are sometimes approached by males during intergroup interactions
(Reichard & Sommer 1997; Bartlett 2009). Disputes generally occur near the boundaries of
the home range when two groups are in visual contact with one another and
typically last around an hour (Bartlett 2003). Most inter-group interactions
are accompanied by vocalizations (Reichard & Sommer 1997). The variability
of the nature of interactions between neighboring groups may partly be the
result of variable social and kin relationships between members of neighboring
groups (Bartlett 2003). However, inter-group interactions can be quite violent,
and there is evidence that wounds incurred in territorial aggression have
resulted in the death of combatants (Palombit 1993). There is seasonal variation
in the occurrence of inter-group encounters and territoriality may function in
resource defense (Bartlett 2009).
Photo: Alan Mootnick
There is no personal leadership of a lar gibbon group, although adult females
lead group progressions most often (Barelli et al. 2008a).
In one long-term study, males dispersed from their natal groups at around 10
years of age and usually attain a territory by replacing one of their resident
adults. Dispersal distances are usually around one or two territories from the
natal territory; averaging in one population 0.71km (0.44 mi) (Brockelman et al.
While lar gibbons usually live in serial monogamous pairs, their reproductive system
is complex and can be polyandrous, sometimes including flexible sexual
relationships which often occur outside of the usual pair bond (Reichard 1995;
Reichard & Barelli 2008). Polygamous mating has also been seen (Bartlett
2007). This is primarily due to the changing relationships among lar gibbons
over their lifetimes, often including successive pairings with different mates
and inclusion in different social group types (Reichard & Barelli 2008).
However, in the case of extra-pair copulation by females, frequency of
copulation remains much higher with the pair-mate than with other males (Barelli
et al. 2008b). Mating occurs in every month of the year, but most conceptions
occur during the dry season (March) with a peak in births during the late rainy
season, in October (Barelli et al. 2008b; Savini et al. 2008).
Lar gibbon females exhibit swelling, protrusion and color change of the
sex-skin beginning several days before ovulation and ending after ovulation,
usually lasting around 7-11 days (Dahl & Nadler 1992; Barelli et al. 2007).
Pregnant females also show sexual swelling, but at random times during pregnancy
(Barelli et al. 2007).
Female solicitation postures include placing herself in front of a male and
looking back at him, presenting her genitals to a male (Ellefson 1974;
Barelli et al. 2008b). Copulation is dorso-ventral, with the male behind the
female (Ellefson 1974). Females may refuse copulation by moving away from the
male, vocalizing, or agonistically refusing the advances of the male (Barelli et
On average, females reproduce for the first time at about 11 years of age in
the wild, much later than in captivity (Reichard & Barelli 2008). The
average reproductive cycle is 21.1 days long (Barelli et al. 2007). At a
minimum, the interbirth interval is 3 years, and averages 41 months (Brockelman
et al. 1998; Reichard & Barelli 2008). Gestation in wild lar gibbons is
around six months (Barelli et al. 2007).
Male-male mounting has been observed among wild male lar gibbons (Edwards
& Todd 1991).
In general, observations of lar gibbon births and infant development are
extremely limited. At birth, lar gibbons weigh on average 383.4g (13.5oz) and
are nearly naked. They are able to vocalize soon after
birth (Crandall 1964; Ellefson 1974; Geissmann & Orgeldinger 1995). At one
study site in Thailand, births showed a peak at the rainy season/dry season
transition in September and October (Reichard & Barelli 2008). In the wild,
infants are carried by clinging to their mother's ventrum (Ellefson 1974). One
infant in the wild did little more than cling to the female for the first
several weeks of life (Ellefson 1974). One wild individual first ingested solid
foods in the fourth month of life, timing also seen in captivity (Ellefson 1974;
Roberts 1983). Also around this time, one wild infant started moving a short
distance from its mother (Ellefson 1974). While uncommon, a measure of parental
care of an infant was seen in captivity including predominantly play behaviors
(Clemens et al. 2008). The ability to brachiate was first seen in a captive
infant around 9 months of age (Roberts 1983).
Infants are weaned around two years of age (Ellefson 1974; Reichard &
Infant mortality is low, under 10% (6.3%) in the first year of life (Reichard
& Barelli 2008).
Photo: Marilyn Cole
Lar gibbons have seven basic vocalization note types. These include the
"wa", "hoo", "leaning wa", "oo", "sharp wow", "waoo" and "other" type of
vocalization (Raemaekers et al. 1984; Clarke et al. 2006). These basic types
are usually assembled into longer phrases (Clarke et al. 2006). There are a
number of types of call bout emitted by lar gibbons in different contexts.
These include normal duets (structured vocalizations given by the mated pair
usually during the mid-morning or afternoon), "ooaa" duets (similar to normal
duets but rarer), calls emitted when disturbed (e.g. when predators are seen, in
times of alarm, during territorial disputes or conflict), adult male solos
(often given early in the day, near dawn or before), subadult male solos, adult
female solos (given by mated females when isolated), and contact calls
(Raemaekers et al. 1984; Raemaekers & Raemaekers 1985). Pair duets are very
loud, and can be heard as far as several kilometers away (Reichard 1998).
Subadult males have been known to interact with one another through solo calling
as well (Raemaekers & Raemaekers 1984a). Once uttered by a pair, "ooaa"
duets are infectious through the forest, often initiating similar vocalizations
from other lar gibbons within earshot (Raemaekers & Raemaekers 1984b).
Most calling occurs in the morning (Yimkao & Srikosamatara 2006).
Vocalization is heard in almost all intergroup encounters, including male solos,
duets, and female solos (Reichard & Sommer 1997). Duet calls probably serve
to reinforce the bond between the mated pair, but also to exclude other gibbon
individuals (Raemaekers et al. 1984). Duets also function in distant vocal
communication with other lar gibbon groups and in territorial defense
(Raemaekers & Raemaekers 1984b). The duet culminates in the female's great
call and is given from anywhere in the territory (Raemaekers et al. 1984). The
great call of an individual female is distinct and unique from the great calls
given by other females (Yimkao & Srikosamatara 2006). In one study, vocal
exchanges between males were the only form of interaction in 20% of inter-group
encounters (Bartlett 2003). In addition, vocal behavior in general functions in
the complex sexual competition within the species (Clarke et al. 2006). With
habitat disturbance due to logging, calling frequency decreases (Johns
Female sexual swellings visibly communicate information about reproductive
condition (Barelli et al. 2007). Male display behavior to increase
conspicuousness includes one-arm dangles, locomotion back and forth around a
particular pathway, and the breaking of branches (Ellefson 1974). Grimaces
(exaggerated smiles) indicate subordination while open-mouth threats indicate an
Branch-jerks occur when a dominant gibbon shakes a branch and
elicits submission from another individual (Ellefson 1974).
Content last modified: November 17, 2010
Written by Kurt Gron. Reviewed by Alan Mootnick.
Cite this page as:
Gron KJ. 2010 November 17. Primate Factsheets: Lar gibbon (Hylobates lar) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/lar_gibbon/behav>. Accessed 2015 April 28.