SOCIAL ORGANIZATION AND BEHAVIOR
The general social structure for macaque species is
multi-male/multi-female with distinct
dominance hierarchies within each sex
(Dittus 2004). Pigtail macaques exhibit this social organization in groups
of up to 81 animals (Oi 1990a). Within these groups, the sex ratio is biased
toward females, which remain in their natal groups
their entire lives (Caldecott 1985; Oi 1990a). Males emigrate from their natal
groups between five and six years of age and temporarily associate with other
social groups before ranging solitarily or permanently immigrating into a group
(Oi 1990a). Adult males are dominant over adult females and males often attack
females and displace them at feeding sites. Groups of females are capable of
attacking adult males, though, and individual females sometimes initiate aggressive
encounters towards lower-ranking males with the help of female relatives (Oi 1990b).
One reason this between-sex aggression may occur is decreased tolerance for competitors.
Females may see low-ranking males not as potential mates but as competitors for food resources. Aggressive behaviors are even more severe between males than between males and females, with the highest-ranking male directing aggression toward lower-ranking males and solitarily ranging males that attempt to join the social group (Oi 1990b). The highest-ranking females in a pigtail macaque group are likely sisters and share similar rank and are highly tolerant of one another. Tolerance is exhibited through grooming, kissing, and feeding together (Oi 1990b).
Though there are multiple males within a group of pigtail macaques, there is
dominance hierarchy among the males
and there is usually a dominant male within the group. When young males immigrate
into a new group, they are the lowest-ranking males and will work their way up
the dominance hierarchy, attempting to secure the position of alpha
male. In captivity, if an adult male is successful at assuming the position
of alpha male after he is placed in a group, he often is responsible for killing
any infants within the group. This infanticidal behavior
has only been recorded in captivity, not in the wild
(Clarke et al. 1995).
Pigtail macaques are not seasonal breeders and mating occurs year-round though
there is a slight peak from January to May (Crockett & Wilson 1980; Rowe
1996). Females reach sexual maturity at three years of age, which is accompanied
by the characteristic anogenital
but compared to M. leonina, M. nemestrina females
have much larger sexual swellings (Maestripieri pers. comm.). Males mature
later, reaching puberty between three and 4.5 years (Sirianni & Swindler
1985). A female solicits a male by approaching him from behind and then passing
directly in front of his face and presenting her rump while looking back over
one shoulder. Females mate with multiple males, both adolescents and adults regardless
of dominance rank, during estrus (Oi 1996). If only a few females in a group
are in estrus, the two top-ranking males are able to monopolize mating with these
females because it is possible for them to keep other males from mating with
one or two females. In fact, if a low-ranking male attempts to solicit or mate
with a female, the alpha male will interfere and act aggressively toward both
the male and female. The higher-ranking males
females if there are more than two in a group at one time,
and lower-ranking males have more opportunities to mate when more estrous females
are present (Oi 1996).
In one study with captive pigtail macaques,
genetic tests of captive pigtail macaques have revealed
that dominance rank did not influence paternity, that is, the highest ranking
individuals did not have the most offspring in the group
(Gust et al. 1996).
These findings cannot be generalized to all pigtail macaque groups and genetic
tests in wild groups of pigtail macaques could lead to new insight into reproductive
success and dominance rank.
While male rank does not guarantee higher reproductive output among male pigtail
macaques, female rank is a factor both in reproductive output and sex of offspring,
according to one captive study. After a gestation
period of 170 days, high-ranking females were more likely to gave birth to female
infants while low-ranking females more often give birth to male infants (Maestripieri
2002). Furthermore, this bias increased with age in both high and low-ranking
females, so that as they age, high-ranking females were even more likely to give
birth to females while low-ranking females are even more likely to give birth
to sons (Maestripieri 2002). One possible reason this pattern was seen could
be that daughters are more energetically expensive to raise as they nurse more
frequently and depend on their mothers for protection for longer because they
remain in their natal group. Males, on the other hand, nurse less frequently
and spend less time near their mothers as they age, eventually leaving their
natal group (Maestripieri 2002). Higher-ranking females have more to gain by
investing in daughters, who will remain in the group and form coalitions with
their female relatives to maintain dominance. Low-ranking females do not gain
as much by having daughters because they are likely to be the target of aggression
from other females and females are energetically expensive to rear (Maestripieri
2002). They give birth to sons that will leave the group and have a chance of
attaining a higher rank than would be possible if they were a female remaining
in her natal group. This is one way that female pigtail macaques increase their inclusive
More research on dominance rank and sex ratio is needed to test these hypotheses.
The interbirth interval for
wild pigtail macaques is between 18 and 24 months, depending on resource availability
Macaque mothers care for their offspring with little or no help from other individuals.
While the majority of care occurs in the first year of life, including nursing, transportation,
and protection, macaque mothers groom and socially support their offspring, especially females,
throughout their lives or until they leave the natal group (Maestripieri 2004). The infancy period
lasts from birth to one year in pigtail macaques and juvenilehood lasts from one to 3.5 years (Oi 1990a).
During the first month of life, pigtail mothers rarely break contact with their infants, but as they age,
infants begin to spend time off of their mother, exploring the surroundings. This is very tentative at
first, but increases after the fifth week of life (Maestripieri 1994a). By the third month of life,
the natal coat of infant pigtail macaques begins to change from
black to the adult olive brown coloration (Maestripieri 1994b).
During infancy, pigtail macaques are subject to being grabbed or seized by other adult females in the group.
All females in the group show great interest in infants, and higher-ranking females often grab lower-ranking
females" infants (Maestripieri & Wallen 1995). These "kidnappings" occur especially while the infant is
moving independently from the mother. If infants are separated from the mother long enough, they are likely
to die from starvation or dehydration (Maestripieri 1994b).
Some researchers (i.e. Crockett & Wilson 1980 and Oi 1990a) describe pigtail macaques as uncharacteristically
quiet monkeys that move through the forest almost silently, with the only sounds coming from juveniles rustling
leaves. They have been observed being silent after fleeing or a group disturbance (perhaps after being startled
by researchers) and are especially quiet after crop raiding and being chased
into forested areas by farmers (Crockett & Wilson 1980; Caldecott 1986). Laboratory and other field studies
show they are not always quiet, and do have a wide range of calls and vocalizations. "Coo" vocalizations are used
as a pigtail macaque group forages and moves through the middle and upper
canopy of the rainforest. These can be short or long in duration and are the most common calls heard in the wild
(Caldecott 1986). Other vocalizations include "squeals," "screeches," "screams," "growls," or "barks." These are
heard in harassed, threatened, or threatening individuals during agonistic
interactions within the group (Caldecott 1986).
Pigtail macaques also have a variety of facial expressions and postural behaviors that communicate status and intent
to other pigtail macaques. "Branch shaking" by males is one display thought to attract the attention of estrous
females as well as threaten peripheral males (Caldecott 1986). A common facial expression unique to pigtail macaques
is the "pucker" or "protruded lips face" seen in both males and females. Males direct "puckers" toward estrous females
as well as other males, with very different results. When adult males "pucker" towards females, they often
copulate directly following the exchange but when a "pucker" is directed toward
another male, the submissive male retreats (Caldecott 1986). The most common facial expression, and one that is seen
throughout macaque species, is the "silent bared teeth" face. Among pigtail macaques this is seen between males,
with the male performing the "silent bared teeth" face always lower-ranking than or submissive to the male to which
the signal is directed (Flack et al. 2000).
In Thailand, pigtail macaques are used by coconut farmers to retrieve fruits from the crowns
of tall palm trees on coconut plantations, a dangerous job for a human but a natural behavior
for a macaque. They are taken from the wild as infants and are raised by humans. By the age
of five years, pigtail macaques are trained to respond to verbal commands, how to choose coconuts
in different phases of ripeness, and how to remove a coconut from the stem (Sponsel et al. 2002).
After a pigtail macaque is trained, it receives food rewards for performing these tasks properly
and an efficient macaque can harvest between 500 and 1000 coconuts per day from a coconut palm
plantation. About half of a family's yearly income may be earned by the pigtail macaque retrieving
the coconuts which are sold at market or used for food and a multitude of other products
(Sponsel et al. 2002).
Content last modified: September 12, 2005
Written by Kristina Cawthon Lang. Reviewed by Dario Maestripieri.
Cite this page as:
Cawthon Lang KA. 2005 September 12. Primate Factsheets: Pigtail macaque (Macaca nemestrina) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/pigtail_macaque/behav>. Accessed 2015 February 1.