Indri (Indri indri)
The average body mass for the adult female is 6.8 kilograms and for the adult male it is 5.8 kilograms (Fleagle, 1999). This species has a dental formula of 2:1:3:3 on both the upper and lower jaws (Ankel-Simons, 2000). The indri has a rudimentary tail, which is elevated during defecation (Pollock, 1975). The indri possesses a dorsal laryngeal sac that assists in the production of the song (Petter and Peyrieras, 1972; Pollock, 1986). Also in the cecum there are microflora to assist in breaking up the cellulose in plant material. The hindlimbs are longer than the forelimbs in this species (Mittermeier et al., 1994). The main pelage coloration of the indri is black with white patches on the crown, flanks, forelimbs or thighs (Mittermeier et al., 1994; Tattersall, 1982). This species has a lighter coloration in the south of its range (Tattersall, 1982). Individuals in the northern ranges have a light colored face ring where individuals in the southern ranges have a black colored face ring (Thalmann et al., 1993). The ears of this species are tufted and black (Mittermeier et al., 1994). The eyes of the indri are yellow (Thalmann et al., 1993). The infants have a pelage coloration of completely black with the white areas (lower dorsal region, sides of arms, eyebrows, throat, and forehead) developing between the ages of 4 and 6 months (Pollock, 1975). Females have a single pair of pectoral mammae (Tattersall, 1982).
This species has two subspecies each having differing pelage colorations:
- Indri indri indri: This subspecies is mainly black all over with a face-ring that is white, full, and broad (Groves, 2001).
- Indri indri variegatus: This subspecies has a occipital cap and collar that are white in color (Groves, 2001). The outer sides to the legs and the lower arms are grayish or whitish in coloration (Groves, 2001).
This species is found in eastern Madagascar in the montane rainforests. The indri occurs from the Mangoro River north to near Sambava, in the reserve of Anjanaharibe-Sud (Mittermeier et al., 1994). Indris live in primary lowland forest and montane rainforests (Evans et al., 1993-1994; Pollock, 1977). From October to December the indri will stay in the lower levels of the canopy to avoid horseflies (Rowe, 1996). This species is found at altitudes up to 1500 meters (Mittermeier et al., 1994).
The indri is found in the following protected areas in Madagascar (Mittermeier et al., 1994):
- Mantady National Park
- Verezanantsoro National Park
- Betampona Nature Reserve
- Zahamena Nature Reserve
- Ambatovaky Special Reserve
- Analamazaotra Special Reserve
- Anjanaharibe-Sud Special Reserve
This species is primarily folivorous, but also eats fruit, seeds, and flowers. Pollock (1975) found that the indri fed on 63 plant species from 39 genera and 19 families, with the families Lauracae and Guttiferacae providing the most commonly consumed species. Males were found to consume more fruit, where females eat more young leaves (Pollock, 1979b). Males also feed for a shorter period of time and consume food more slowly than adult females and young offspring (Pollock, 1977). Powzyk and Mowry (2001) found that at Mantady National Park the bulk of the diet of the indri consisted of immature leaves. Indri groups were found to consume soil each day (Pollock, 1975). The indri is known to feed on the fruits and leaves of the Rara tree (Bronchoneura sp.), Menahihy (Campylospermum sp.), Voapaka (Uapaca sp.), Hazinina (Symphonia sp.), Molopangady (Alberta sp.), Zanamalotra (Dialium sp.), Tarantana (Rhus tarantana), Mampay (Cynometra sp.), Sadodok'ala (Gaertnera sp.), and Ramy (Canarium madagascariensis) at Betampona Natural Reserve (Britt et al., 1999). At Anjanaharibe-Sud Special Reserve indris mainly consume the ripe fruits of the Vongomena (Symphonia sp.), Vahamivohotra, Vongo (Symphonia clusoides), leaves of Tavolo (Ravensara madagascariensis), and the buds of Tafonana (Mespilodaphne faucheri) (Thalmann et al., 1993). Pollock (1977) found that the species Ravensara pervillei was foraged upon whenever a group came in contact with them.
Leaves are picked off of the tree, but fruit is taken by the mouth and then transferred to the hand (Pollock, 1975). Evans et al. (1993-1994) also found that red, young leaves were picked off with the mouth. Young leaves on saplings are preferred foods and if an indri is too large to be supported on the sapling's trunk, it will pick at the leaves from an adjacent larger tree (Pollock, 1977). Three limbs are always used when feeding, supporting the individual as they forage (Pollock, 1975). The tooth-comb is used to scoop out the endosperm of unripe fruit (Pollock, 1977). Mature leaves are eaten in bites from the side or the apex of the leaf (Pollock, 1977). Indris feed at all levels (2-40 meters) in the forest (Pollock, 1977). At Analamazoatra Special Reserve the indri would spend 35% of the time in the middle level, 17% of the time in the top level, and 17% of the time in the bottom level of the canopy feeding (Pollock, 1977).
Group members will awake, stretch, and consume the nearest available food source, often in the sleeping tree (Pollock, 1975). Then group members will urinate and defecate synchronously, often standing on the same horizontal support and defecating in a defecation area (Pollock, 1975). Feeding then commences, occurring at a constant rate over the rest of the day (Pollock, 1975). But when no concentrated food source is present, the group ranging behavior is less predictable and more scattered (Pollock, 1979a). This species will range more during the cold, dry months than during the warm, wet summer months (Pollock, 1979a). Ranging behavior tends to depend upon food distribution (Pollock, 1977). A grooming session will end the feeding, with the group resting until morning (Pollock, 1975). The indri sleeps in trees ranging in height from 30 to 100 feet, with the group being spread out over 100 meters (Pollock, 1975). They will usually sleep on horizontal sleeping supports (Pollock, 1975). Indris will sleep two individuals huddled together, but never more than two (Pollock, 1975). Infant indris will first sleep with their mothers until about the second year, and the next youngest offspring will usually sleep with the adult male (father) of the group (Pollock, 1975). Females will attack males that come to close to them when they are sleeping (Garbutt, 1999). Group sizes at Anjanaharibe-Sud Special usually are made up of 2-3 individuals, but groups of six individuals have been reported (Thalmann et al., 1993). At Ambatovaky Special Reserve, the mean group size was found to be 2.6 individuals (Evans et al., 1993-1994). The indri is an arboreal and a diurnal species.
The indri mainly moves by leaping between large stems and trunks (Walker, 1979). When leaping contact is first made with the hindfeet (Napier and Walker, 1967). The indri is capable of horizontal leaps of 10 meters (Pollock, 1986b). This species will use quadrupedal locomotion when crossing large gaps in the forest moving over thin or flexible boughs (Walker, 1979). Bipedal locomotion is used when moving on the ground (Walker, 1979). The indri will feed by sitting on vertical trunks and hanging suspended by all fours (Walker, 1979). This species will rest by holding the body against a vertical trunk or by holding a horizontal or diagonal branch with all four extremities with the hindlimbs flexed around the forelimbs (Walker, 1979). Infant indris begin practicing leaping at 4-5 months of age, and by 8 months the infant can land successfully (Pollock, 1975). At one year of age the young indri has refined locomotor behavior and has the ability to calculate optimal routes (Pollock, 1975).
This is a monogamous species. The basic group of the indri is composed of the adult male, adult female, and their offspring from various seasons (Pollock, 1975). Females are dominant over males with having priority access to food resources (Mittermeier et al., 1994; Pollock, 1979b). Males also have never been seen to displace females (Pollock, 1979b). Females have a tendency to forage on young leaves where males consume more fruits (Pollock, 1979b). Females also lead group progressions on a regular basis (Pollock, 1979b). Social activities, i.e. grooming, playing, aggressive, and sexual behavior, account for 2% (6 to 13 minutes) of the daily activity of the indri (Pollock, 1979b).
This species is highly territorial, but there is a small amount of overlap with the home ranges of adjacent groups on the periphery (Pollock, 1975, 1979a). In the overlap area, groups will engage in vocal battles using the song vocalization and groups will defend their territory (Pollock, 1975). Groups will scent mark to demarcate their territory (Pollock, 1975). Males will sometimes disregard territorial boundaries and range freely throughout various groups' territories (Pollock, 1979a).
Most aggression that occurs in the indri happens during feeding (Pollock, 1979b). Aggression during feeding occurs over food competition and when an individual becomes disrupted from their feeding support branch by another (Pollock, 1979b). Aggression at food sources was found to occur when there are conditions that are crowded (Pollock, 1977). Adult males will be displaced from feeding sites when an adult female approaches them, moving to lower branches in the tree to avoid possible agonistic attacks (Pollock, 1979b).
Social play is found in the indri, with most play bouts performed by the young (Pollock, 1975, 1979b). This behavior consists of wrestling and affiliative and agonistic behavior patterns may occur throughout bouts (Pollock, 1975). A playful wrestling bout can last from a few seconds to 15 minutes during the months of summer (December to March) (Pollock, 1979b).
song: This call lasts from 60 to 150 seconds and consists of a series cries or howls that vary in frequency from 500 and 6000 hertz (Pollock, 1975). Song is often introduced by roar, which is started by the adult male of the group (Pollock, 1986a). A pause of 0.5 to 2 seconds separates the introduction roar from the start of the song (Pollock, 1986a). Each individual call of the song can last from 1 to 4 seconds (Pollock, 1986a). There are three types of calls that make up the song (Pollock, 1986a). Type 1 calls are long, low, have a fundamental frequency of 750 hertz, have little frequency modulation, and are only emitted by adult males (Pollock, 1986a). Type 1 calls are twice as long as other song component calls (Pollock, 1986a). Type 2 calls are amplitude modulated, end at a pitch higher than when they begin, the energy resides between 700 and 3000 hertz, last from 1.2 to 2.0 seconds, and is emitted by all singing individuals (Pollock, 1986a). Type 3 calls consist of a series of 3-4 successive calls that each begin with a lower frequency than the call that comes before it (Pollock, 1986a). Type 3 calls have the same duration as type 2 calls, and this call is emitting by all participating group members but the adult female will usually emit this call earlier than other group members (Pollock, 1986a). When song is sung by groups, it will sometimes be synchronized (Pollock, 1986a).
This call is emitted throughout a group's territory (Pollock, 1975, 1986a). The call is most optimally emitted from the tops of trees (Petter and Charles-Dominique, 1979). This call varies amongst groups, so that each group may be distinguished by its song (Pollock, 1975). The frequency that a group will emit this call depends upon the season, weather, and proximity of adjacent groups (Pollock, 1975, 1986). When rain will fall, the indri will emit song less but will compensate by singing more during days that have more brightness (Pollock, 1986a). The indri will usually utter this call in the morning (Pollock, 1986a). This call is heard most frequently in the months of December and January (Pollock, 1986a). Oliver and O'Connor (1980) also found that as the mean temperature increased the rate of emitting song also increased. During April this is heard at night at Anjanaharibe-Sud Special Reserve (Thalmann et al., 1993). At Beanana, Analamazoatra, and Vohidrazana song is heard at night during late Novmeber and December (Thalmann et al., 1993; Pollock, 1986a). The presence of a full moon at night may elicit song (Oliver and O'Connor, 1980). Song will start earlier and continue later in the summer months (Pollock, 1986a). All members of the group will participate in song, but only the adult female will sing throughout the song (Pollock, 1986a). Young individuals will only participate in roar and the first seconds of the song (Pollock, 1986a). Subadults (age 3-6 years) will participate in song up to the first half (Pollock, 1986a). Feeding can occur between howls during the emission of this call (Pollock, 1986a). This call functions to communicate territoriality, reunites temporarily dispersed group members, and is a response to aerial predators, airplanes, and thunder (Pollock, 1975). This call may also communicate the reproductive status of group members (Pollock, 1975). When sung in the morning, song may function to inform other groups of the present location (Pollock, 1986a). Song may induce a nearby group to respond with a similar call (Oliver and O'Connor, 1980). Choruses of one or more neighboring groups can occur (Oliver and O'Connor, 1980).
roar: This is a loud barking call emitted by all group members (Pollock, 1975). This call will sometimes precede song but also is an alarm call against aerial predators (Pollock, 1975; Oliver and O'Connor, 1980). Thalmann et al. (1993) referred to this call as waa notes.
hoot: This call is an alarm call against ground predators and is emitted by adult males and sometimes by the oldest male offspring (Pollock, 1975). Thalmann et al. (1993) called these honks and reported that they may be emitted in the form of a duet by two individuals. Ruffed lemurs, Varecia variegata, have been observed to respond to this alarm call (Raxworthy and Stephenson, 1988).
hum: This is a soft call that announces imminent movement (Pollock, 1975).
grunts: This call is emitted when an individual is frightened or anxious at a low intensity (Pollock, 1975).
kisses: This call is emitted when an individual is frightened or anxious at a medium intensity (Pollock, 1975).
wheezes: This call is emitted when an individual is frightened or anxious at a high intensity (Pollock, 1975).
Olfactory communication is important for this species.
cheek-marking: This is done by the males to set boundaries for the group. The glands associated with this behavior are located on the side and underneath the muzzle (Pollock, 1975).
genital marking: This behavior is performed by adult males to demarcate the territory (Ranaivosoa, 1998).
social grooming: This is when one individual will remove dead skin and/or parasites from another. In the indri this behavior is concentrated on the head and neck, and grooming partners will alternate grooming bouts (Pollock, 1975). Grooming is done on another by using the tooth-comb and the tongue on the face, neck, ears, and back (Pollock, 1979b). Reciprocal grooming occurs, but not simultaneous grooming (Pollock, 1979b).
This species gives birth to a single offspring at irregular intervals of about three years (Klopfer and Boskoff, 1979). Breeding occurs in the months of December and January (Pollock, 1986a). The birth season for this species is in May (Pollock, 1975). Although Thalmann et al. (1993) found that at Anjanaharibe-Sud Special Reserve the birth season started in December. The gestation period is 120-150 days (Mittermeier et al., 1994). The interbirth interval is 24-36 months (Rowe, 1996). Indris reach sexual maturity between the ages of 48-84 months (Rowe, 1996). Infants will suckle three or four times a day (Pollock, 1975). Suckling ceases at one year of age (Pollock, 1975). Until the age of 4-5 months infants will be carried on the ventral side of the mother when they switch to the dorsal side (Mittermeier et al., 1994; Klopfer and Boskoff, 1979). Although at two years the infant moves and feeds separately from the mother, they still maintain a close relationship in that they maintain a close proximity to each other (Pollock, 1975). Males will smell and lick the genitalia of the female before mounting (Pollock, 1975). Copulation will sometimes occur with the indris hanging under a branch with the legs expanded and copulating in a ventro-ventral position (Thalmann et al., 1993).
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Last Updated: October 8, 2003.
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