AppearanceAlong with the diademed sifaka, the indri is the largest lemur still in existence. It has a head-body length of 64–72 cm and can reach nearly 120 cm with legs fully extended. It can weigh between 6 and 9.5 kg , though the average is on the lower end of the range.
The indri is a vertical clinger and leaper and thus holds its body upright when traveling through trees or resting in branches. It has long, muscular legs which it uses to propel itself from trunk to trunk. Its large greenish eyes and black face are framed by round, fuzzy ears that some say give it the appearance of a teddy bear. Unlike any other living lemur, the indri has only a rudimentary tail. The silky fur is mostly black with white patches along the limbs, neck, crown, and lower back. Different populations of the species show wide variations in color, with some northern populations consisting of mostly or entirely black individuals. The face is bare with pale black skin, and it is sometimes fringed with white fur.
Due to these color variations, Colin Groves listed two subspecies of the indri in 2005: The dark ''Indri indri indri'' from the northern part of its range and the relatively pale ''Indri indri variegatus'' from the southern part. Later editions of ''Lemurs of Madagascar'' by Russell Mittermeier ''et al.'' do not recognize this classification, and recent genetic and morphological work suggests the variation in the indri is clinal.
NamingThe name "indri" most likely comes from a native Malagasy name for the animal, ''endrina''. An oft-repeated, but probably incorrect story is that the name comes from ''indry'' [ˈiɳɖʐʲ], meaning "there" or "there it is." French naturalist Pierre Sonnerat, who first described the animal, supposedly heard a Malagasy point out the animal and took the word to be its name. The Malagasy name for the animal is ' [bəbəˈkut]. ''Babakoto'' is most commonly translated as "ancestor" or "father", but several translations are possible. "Koto" is a Malagasy word for "little boy", and "baba" is a term for "father", so the word "babakoto" may be translated as "father of a little boy." The father-son dynamic of many of the babakoto origin myths helps to explain the Malagasy name.
DistributionThis lemur inhabits the lowland and montane forests along the eastern coast of Madagascar, from the Réserve Spéciale d’Anjanaharibe-Sud in the north to the Mangoro River in the south. They are absent from the Masoala Peninsula and the Marojejy National Park, even though both regions are connected to forests where indri do occur less than 40 km away.
StatusThe first film of indri was obtained by using tape lures, on an expedition forming the basis of David Attenborough's 1961 BBC series ''Zoo Quest to Madagascar''
The indri is an endangered species. The primary threats to its existence are habitat destruction and fragmentation due to slash and burn agriculture, fuelwood gathering, and logging. This kind of destruction occurs even in protected areas.
The indri is also widely hunted, despite the many origin myths and traditional taboos which hold it sacred. Cultural erosion and immigration are partly to blame for the breakdown of traditional beliefs. In some cases, Malagasy people who resent the protective ''fady'' find ways to circumvent them. People whose ''fady'' forbid them from eating the indri may still hunt the lemurs and sell their flesh, and those forbidden to kill the indri may still purchase and consume them. Indri meat is prized as a delicacy in some regions.
Only one indri has lived over a year in captivity and none have bred successfully while captive.
BehaviorThe indri practices long-term monogamy, seeking a new partner only after the death of a mate. It lives in small groups consisting of the mated male and female and their maturing offspring. In the more fragmented forests of their range, the indri may live in larger groups with several generations. Habitat fragmentation limits the mobility and capacity of these large groups to break into smaller units.
It is common for groups to move 300-700 m daily, with most distance travelled midsummer in search of fruit. The indri sleeps in trees about 10-30 m above ground and typically sleep alone or in pairs. It is common for young female indri's, occasionally adult females, to silently play wrestle anywhere from a few seconds up to 15 minutes. Members of a single group will urinate and defecate jointly at one of their many selected areas of defecation in their territory.
The indri is well known for its loud, distinctive songs, which can last from 45 seconds to more than 3 minutes. Song duration and structure varies among and even within groups, but most songs have the following three-phase pattern.
Usually, a "roar sequence" lasting for several seconds will precede the more characteristic vocalizations. All members of the group participate in this roar, but the song proper is dominated by the adult pair. They follow the roar with a "long note sequence", characterized by notes of up to 5 seconds in duration. After this is the "descending phrase sequence". The wails begin on a high note and become progressively lower-pitched. It is common here for two or more indri to coordinate the timing of their descending notes to form a duet.
Different indri groups typically sing sequentially, responding to one another. As well as solidifying contacts between groups, the songs may communicate territorial defense and boundaries, environmental conditions, reproductive potential of the group members, and warning signals. The indri may sing after disturbances such as thunder, airplanes, bird calls, and other lemur calls. A group will sing almost every day, up to seven times daily. The peak singing hours are between 7 and 11 AM. Daily frequency of song is highest during the indri's breeding season from December to March.
Several other indri vocalizations have been identified. The "roar" is also used as a warning signal for aerial predators such as hawks. The indri emit a "hoot" or "honk" to warn of terrestrial predators such as the fossa. Other vocal categories include the "grunt", "kiss", "wheeze", and "hum". The purpose of these is still not entirely clear.
In order to amplify their song, the indri will move to the tree top before they call which allows them to be heard up to 3-4 km away.
ReproductionIndri's reach their sexual maturity between the ages of 7-9. Female indri bear offspring every two to three years, with a gestation period of approximately 120–150 days. The single infant is usually born in May or June. The mother is the primary caregiver, though the father assists, remaining with his mate and offspring. Infants are born mostly or completely black and begin to show white coloration between 4 to 6 months of age. The infant will cling to its mother's belly until it is four or five months old, at which time it is ready to move onto her back. The indri begins to demonstrate independence at eight months, but it will not be fully independent from its mother until it is at least two years old. The indri reaches reproductive maturity between seven and nine years of age: a relatively slow rate.
FoodThe indri is herbivorous and primarily folivorous. It prefers young, tender leaves but will also eat seeds, fruits, and flowers. Female indri seem to have greater preference for immature leaves than males do and will spend more time foraging among them. A wide variety of plant species are consumed, with members of the laurel family featuring prominently in the diet. The indri consumes little non-tree vegetation.
To feed, the indri plucks off a leaf or other plant part with its teeth. It uses its hands to pull tree branches closer to its mouth.
Reproductively mature females have priority access to food sources, therefore they forage higher in the trees than males.
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