SOCIAL ORGANIZATION AND BEHAVIOR
Owl monkeys live in closely-knit social groups of two to five
individuals made up of one adult of each sex and young of
various ages (Wright 1978; 1989; 1994; Fernandez-Duque et al. 2001).
While researchers long assumed that owl monkeys lived in family groups,
because there is always a single reproductive female and a single reproductive
adult male that cares for the offspring, research from at least one species, A.
azarae, reveals that the social structure may be more flexible than a monogamous
family group. Frequently, resident adults are displaced by other same-sexed
adults which then assume the breeding and care position in the social group.
Males are equally as likely as females to be replaced (Fernandez-Duque in press).
This process of replacement is characterized by high levels of physical aggression
between the new adult attempting to displace the resident adult male or female
and can lead to permanent disfigurement or even death of the resident owl
monkey (Fernandez-Duque 2004).
Aotus groups move
together cohesively, with individuals never more than ten meters (32.8 ft) from
one another. Aggressive or agonistic behavior between group
members is exceptionally rare (Wright 1981; 1994). Owl monkeys exhibit
some inter-group aggression at their home-range boundaries and meetings
at fruit trees on the perimeter of their territories include loud
vocalizations, stiff-legged jumping displays, chasing, wrestling, and piloerection. These encounters
usually only last about ten minutes, after which neither group "wins"
but rather retreats into its own territory (Wright 1994). Peaks of
social behavior, including inter-group aggression, occur most often when
the moon is bright (Wright 1989). Other social behaviors seen in owl
monkeys include grooming and play. Grooming is not often seen (less
than one grooming bout per month occurs between adults within a group),
but play is an important social behavior that is especially prevalent on
bright nights. The adult male and his offspring play by wrestling and
chasing, and often exhibit patterns of "pounce and retreat" and "rough
and tumble" play four to five times per day in bouts of five to 20
minutes. Adult females rarely play with their offspring (Wright 1981).
Photo: Marilyn Cole
Because the primary social unit is the adult pair, both males and
females disperse from their natal
groups when they reach sexual maturity to find mating opportunities
and start their own family groups. Both males and females leave the
group between two and three years of age and range solitarily until they
can find mates and establish a new territory (Fernandez-Duque &
Huntington 2002; Fernandez-Duque in press). While establishment of new groups is not well-studied,
subadult group members usually lag behind other group members during the
month prior to their dispersal and spend more time away from the group,
vocalizing and even sleeping in different trees, indicating they are
preparing to leave the group and find a mate (Wright 1994;
Fernandez-Duque & Huntington 2002). The timing of dispersal is also
fairly uniform across groups, between August and January, and could
either be related to the presence of new infants within the group or an
attempt to find a mate before the mating season begins in May
(Fernandez-Duque & Huntington 2002).
REPRODUCTION
Almost all of the information about owl monkey reproductive
characteristics comes from captive studies of the animal and new
research on wild owl monkeys is beginning to reveal a very different
picture. In captivity, Aotus has a monogamous mating
system and the long-term bond between the adult pair probably lasts
for life (Kinzey 1997). In the wild, the bonds between adult owl monkeys are dynamic and pairs
separate regularly (Fernandez-Duque 2004). Male owl monkeys enter puberty at an early age,
about one year old, when they begin to adopt physical characteristics of adult
males including testicular growth and activation of the scent glands
located under the base of the tail (Dixson 1994). As adults, male owl
monkeys have extremely low sperm counts, probably as an adaptation to
their monogamous mating system; only reproducing with one female, one
time per year means it is unnecessary and energetically wasteful to
produce high levels of sperm. Females are capable of reproducing as
young as two years old, but normally do not give birth until about three
years old (Gozalo & Montoya 1990). Physical examination of wild-caught A. a.
azarae reveal that individuals do not reach adult body mass or have fully adult
characteristics until about four years of age and age at first reproduction is at about
five years (Fernandez-Duque in press). The ovarian cycle lasts about 16 days and
menstruation does not occur in female owl monkeys. Mating occurs very
infrequently both in the wild and in captivity and seems to be timed
with ovulation (Dixson 1994;
Fernandez-Duque et al. 2002). Once pregnant, gestation lasts 133 days
and Aotus births are almost always singletons although twins are occasionally
seen (Dixson 1994). In captivity, births occur year-round, but there
is consistent peak in births from October to January. Among wild owl
monkeys in the Argentinean Chaco, births coincide with the beginning of
the rainy season, between late September and late November, and may be
related to temperature and light conditions. Females that mate in April
or May have a wide resource base available to support them during their
energetically expensive pregnancy while infants born at the beginning of
the rainy season will be mature enough to survive the extreme
temperature drops seen in the dry season in May (Fernandez-Duque et al.
2002). Changes in photoperiod are probably the cue for mating to begin
which is why similar peaks in births are seen both in the wild and in
captivity (Fernandez-Duque et al. 2002). The interbirth interval is about 12 months
for both wild and captive owl monkeys (Dixson 1994; Fernandez-Duque et
al. 2002).
PARENTAL CARE
Aotus azarae boliviensis
Photo: Rosie Bolen
Among A. azarae studied in the Argentinean Chaco, rates of
infant survival to six months are extremely high, around 96%, while
in captivity, survival rates through the first year are about 85.8%
(Gozalo & Montoya 1990; Fernandez-Duque et al. 2002). These high
survival rates may be attributed to low incidences of predation and
almost constant parental care. Owl monkey males are extremely
involved in the socialization and care for dependent offspring. Researchers have
long assumed that this pattern of parental care is seen because males are certain
of their paternity because of their mating patterns and because of the potential
benefits to the infant (Wright 1981). Genetic tests have not been conducted to
confirm that male caregivers are fathers and until this is done, other explanations
for this behavior should also be explored (Fernandez-Duque pers. comm.).
Male owl monkeys that constantly carry dependent
offspring may be better equipped to flee from predators or danger than a
lactating female of equal size. Because lactation is nutritionally
expensive and energetically taxing, females may lack the energy
necessary to run with infants that are relatively large compared to
their body size (Wright 1984). The infant, therefore, gains an advantage if being carried by an adult male compared to its mother.
Newborn owl monkeys weigh, on average, 96.5 g (3.40 oz) and instinctively ventrally cling to the mother. The
infant will exhibit this pattern of attachment until about three to four
weeks of age, when it will begin to cling dorsally to its carrier
(Dixson 1994). Developmental stages have been observed in captivity. Starting on the first day of life, the father begins to
carry the infant, and though he will carry the infant almost exclusively
for the first 2 months of life, the mother carries and nurses the
neonate in the first week of life (Wright 1984; Dixson 1994). After the
first week, the mother only carries the infant when it nurses,
approximately 10 to 20% of the time, the remaining 80 to 90%
of its life is spent on the father (Wright 1986). Beginning as early as
22 days or as late as 46 days, infants get off the carrier and begin to
eat solid food as a supplement to nursing (Dixson 1994). As they age,
infants are carried increasingly less such that by five months of age,
they are totally independent. As they gain this independence though,
there are some conflicts between the father and infant starting at about
four months; conflicts over carrying include the infant holding on to
the father tightly while he attempts to bite or push the infant off.
During this time, there is very little carrying by the father, but the
infant still rides on his back as the group travels between trees that
are between three and four meters apart (9.84 and 13.1 ft) (Wright 1984). Even though
infants travel independently by five months of age, they are not weaned
completely until about seven months and in the instance of any
disturbance or stressor, they will return to the parents for support
(Dixson 1994). Older siblings that are still in the group when an
infant is born take turns carrying it, but they are limited to carrying
during the first four weeks of life, after which the infant is too big
for them to support (Wright 1984).
COMMUNICATION
Owl monkeys communicate through chemical signaling and scent marking,
vocalizing, and by using some visual cues (Wright 1994; Bolen &
Green 1997). Specialized scent glands under the base of their tails
secrete chemical signals that convey information to other individuals
including sexual identification and route-marking from sleeping sites to
food resources (Wright 1989; 1994). They also exhibit a behavior known
as "urine washing" in which they urinate on their feet and hands and as
they walk over branches, leaving a scented path (Wright 1981). Their
honed sense of smell may also help them distinguish ripe from unripe
fruits in an environment in which color is dulled (Wright 1989).
Unlike their highly developed sense of smell, the auditory system
among owl monkeys is unspecialized compared to other primates. However,
they do have a specialized throat pouch which inflates and increases the
volume and power of calls (Wright 1981). They have not been observed giving a territorial
call like other monogamous primates such as gibbons (Hylobates
species), but their vocal repertoires may serve to reinforce bonding between
individuals of a group as well as inter-group interactions at home range
boundaries (Wright 1981). The aggressive call or "war whoop" of owl
monkeys is a call consisting of a series of a dozen low notes or grunts
which increase in volume and power into hoots; this call is exhibited by
both sexes and heard only during direct conflict with another group.
Subadult males and females use the same type of call in a shorter series
of three to five hoots as a long-distance contact call when they are
looking for a mate (Wright 1981; Kinzey 1997). The generalized alarm
call of the owl monkeys is a series of "sneeze-grunts" while softer
calls that sound like purrs are used to reinforce bonds between group
members or alert them to desirable food sources. When infants express
desire for food or contact to their parents, they squeak loudly (Wright
1981).
Content last modified: July 18, 2005
Written by Kristina Cawthon Lang. Reviewed by Eduardo Fernandez-Duque.
Cite this page as:
Cawthon Lang KA. 2005 July 18. Primate Factsheets: Owl monkey (Aotus) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/owl_monkey/behav>. Accessed 2013 May 20.
