SOCIAL ORGANIZATION AND BEHAVIOR
Indri group sizes are small, averaging only 3.1 individuals (usually between
two and six individuals) and typically containing a reproducing pair and their
offspring (Petter & Peyriéras 1974; Pollock 1975a; Powzyk &
Thalmann 2003). Group members usually remain within 100m of another member of
the group (Pollock 1975a).
Photo: Kevin Schafer
Several short studies of calling in indris have shown that calling bouts in
the species may play a role in their territorial defense and announcement, as
each group defends an exclusive territory (Oliver & O'Connor 1980; Pollock
1979a; Geissmann & Mutschler 2006; Mittermeier et al. 2006; Powzyk &
Mowry 2006). Although evidence is still somewhat ambiguous, the limits of each
group's territory seem to be for the most part maintained and respected through
some means which may also include scent-marking (Pollock 1975a; 1979b). It is
possible that physical confrontations also play a role (Pollock 1975a). Most
calling is in the morning (with the most in the summer), usually ending by
around noon (Thalmann et al. 1993; Powzyk 1997 cited in Powzyk & Thalmann
2003; Geissmann & Mutschler 2006; Mittermeier et al. 2006).
Adult females are dominant to adult males (Pollock 1979a). The majority of
aggression is related to feeding and in such aggression females usually come out
on top (Pollock 1979a; 1979b). In fact, females seem to dictate exactly how
much feeding males actually perform (Pollock 1979b). Affiliative interactions
between indris include allogrooming (of inaccessible body areas by others), and
play-wrestling (mostly young individuals) (Pollock 1979a).
Males might migrate to form new groups (Pollock 1986).
Data on reproduction in indris are extremely limited, likely in part due to
the difficulties with captive management. Indris are monogamous, and adults
will find new mates only upon death of a previous one (Powzyk & Thalmann
2003). Anecdotal observations describe a suspensory ventro-ventral copulation
posture (Thalmann et al. 1993). Males initiate copulation by licking and
smelling of the female genitalia (Pollock 1975a). Mating and births are
seasonal, with births falling in May and June and Mating in December through
March (Garbutt 1999; Mittermeier et al. 2006).
Sexual maturity is reached between 7 and 9 years old (Garbutt 1999).
Gestation is estimated at 119-154 days (Pollock 1975a). In the wild, the
interbirth interval is around two or three years (Powzyk & Thalmann
Akin to the reproductive data, information about the development of infants
and parental care is extremely limited. For the first 2 or 3 months of life,
infants are all black (except for the white patch on the torso), and then change
to a more adult-like pelage (Powzyk & Thalmann 2003; Powzyk & Mowry
2006). The primary caregiver is the mother (Powzyk & Thalmann 2003).
Births usually occur in May or June (but can as late as August) (Garbutt 1999;
Mittermeier et al. 2006). One wild infant suckled in bouts three or four times
a day. Carrying is on the mother's ventrum before 4 or 5 months old, after
which the infant rides on the mother's back. The first transfer off the mother
is between 4-6 weeks of age, and gnawing of solid food commences around two
months old. At an age of 8 months old, the infant moves by itself. Weaning is
before one year of age (Pollock 1975a).
In general, indris use calling more than scent-marking in communication, and
vocalizations may be audible for over 2 kilometers (1.2 miles) (Oliver &
O'Connor 1980; Powzyk & Mowry 2006). Calls are made louder by a laryngeal
sac possessed by the species and are generally emitted as highly variable long,
loud songs, and by adults of both sexes (Petter & Peyriéras 1972;
Thalmann et al. 1993; reviewed in Geissmann & Mutschler 2006). Loud calls
are divided into three general classes of vocalization: "waa notes," "the song
proper," and the "descending phrase sequence" (Thalmann et al. 1993). Indri
songs can last anywhere between 40 seconds to around 4 minutes, followed by a
resumption of normal activities (Pollock 1986). Calling in indris can be
spontaneous, in response to the calls of other groups (contagious calling, in
which songs can be heard sequentially through the forest as each neighboring
group participates), or more rarely in response to disturbance (Oliver &
O'Connor 1980; Pollock 1986; Powzyk & Thalmann 2003; Powzyk & Mowry
2006). Calling usually occurs at least once per diurnal cycle, but the total
number of calls heard varies by the day (Pollock 1986). There is seasonal
variation in the emission of indri songs, with the most songs heard in the
middle of the astral summer (December and January) (Pollock 1986).
Functions of indri songs are generally unclear, but may include communicating
information about reproduction, mated status, group size, age and sex, about
territorial extent, in disputes about territory, or about territorial location
and presence in the forest (Oliver & O'Connor 1980; Pollock 1986; Powzyk
1997 cited in Gould & Sauther 2007; Powzyk & Mowry 2006). Calling also
may function in individual recognition, and to bring group members together
(Pollock 1986; Powzyk & Mowry 2006). Predator alarm calls are "roars" which
are also often heard directly preceding the longer songs (Pollock 1986). Honks
also probably show alarm (Thalmann et al. 1993). Calling at night is not
unheard of, even though the animals are inactive during that time (Pollock 1986;
Thalmann et al. 1993). Less calling is heard during inclement weather (Pollock
1986). Other types of call include "grunts," "kisses," and "wheezes," as well
as "hums" that are heard before group movement (Pollock 1975b cited in Powzyk
& Thalmann 2003).
Anogenital scent-marking has been observed in indris (Powzyk 1997 cited in
Powzyk & Mowry 2006).
Content last modified: July 1, 2010
Written by Kurt Gron. Reviewed by Joyce Powzyk.
Cite this page as:
Gron KJ. 2010 July 1. Primate Factsheets: Indri (Indri indri) Behavior . <http://pin.primate.wisc.edu/factsheets/entry/indri/behav>. Accessed 2015 December 1.