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Indri
Indri indri

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).

REPRODUCTION

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 2003).

PARENTAL CARE

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).

COMMUNICATION

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).

LISTEN TO VOCALIZATIONS

Indri indri: Vocalization (Kenneth Glander/Duke University)

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: May 20, 2009

Written by Kurt Gron.