Subspecies: I. i. indri,
The genus Indri is monotypic with the one species divided into two subspecies (Groves 2005).
The largest of the Malagasy lemurs is the indri (some argue that this distinction is shared with Propithecus diadema diadema), a unique animal that is the sole lemur with a short, vestigial tail that appears stump-like. Indris weigh on average 6.8 kg (15.0 lb), with an average head and body length of 62.6 cm (24.6 in) and a short tail averaging 5.3 cm (2.1 in). Females weigh more than males. All indris have yellow eyes and large black ears. The species also possesses a toothcomb which it uses for grooming and feeding comprised of four teeth, two incisors and two canines. Overall, they are black with some white pelage, although the exact mixture of black and white is variable by location and by individual within their north/south range. Individuals in the south have more white in their coloration. Pelage is graded between northern and southern forms, with intermediate coloration seen between the northern and southern extremes. Northern indris (
Indris are among the most arboreal of the Malagasy lemurs (usually avoiding the ground), moving through their environment through ricochetal leaping or vertical climbing and leaping. Overall, their locomotion consists mostly of leaping between tree trunks, during which the body is held close to vertical with the arms outstretched. There are some reports of terrestrial bipedal locomotion. Indris are extremely hard to maintain in captivity and currently there are none in zoos worldwide.
Like all lemurs, indris are found only on
Indris are found in the primary and secondary eastern tropical rainforest or humid forests of Madagscar, in both lowland mid-altitude and montane forests and including some disturbed habitats. They are often found in mountainous habitats or habitats on steep terrain with numerous ridges and valleys. Indris are found to range from nearly sea level to an altitude of 1800 meters (5905.5 feet).
At the Betampona Reserve in eastern Madagascar, temperatures average 21°C (69.8°F) (averages are cooler between June and September, averaging 18°C (64.4°F)) with an annual rainfall of 412.9 cm (162.6 in). The most rain falls between January-March and June-August with no true dry months, although October and November are drier than the rest of the year.
Indris are predominately folivorous, consuming predominantly leaves (mostly young) but also fruits, seeds, and flowers. They are both dentally and digestively adapted for their diet. At the
Indris feed by breaking off the desired part of the plant with their mouth, not with their hands. Most feeding occurs while sitting or standing above a branch (78%) but may also occur while clinging vertically to a substrate (21.6%) (Britt et al. 2002).
Indris are strictly diurnal with the daily activity period usually lasting between only 5-11 hours, with longer activity periods seen in the summer (Pollock 1975a; 1977; Powzyk & Mowry 2006). At Betampona for example, indris did not start feeding before 9am and were finished with all activity by 3pm. Feeding usually comprises around 40% of the daily activities, and the species rests a large proportion of their time as well, often around 8 of the daylight hours. Social activities comprise only a very small portion of the daily activities; in one study only 2%.
In the morning, group members usually start activity at around the same time followed by short feeding bout and a short group movement and synchronous group defecation and urination. All-day constant feeding then ensues until near the end of the activity period, when there is a grooming session and activity is finished for the day. Indris sleep in trees between 30 and 100 feet (9.1 and 30.5 meters) off of the forest floor.
Home range and daily path vary by location and differences are mostly due to habitat quality. Recorded average home ranges are 0.27 km² (0.1 mi²) but other recorded group ranges included 0.15., 0.18, 0.18, and 0.3 km² (0.06, 0.07, 0.07 and 0.12 mi²) and perhaps as high as 0.4 km² (0.15 mi²). The indri daily path is usually around 774 m (2539.4 feet), but can range between 300 and 700 m (984.3 and 2296.6 feet). The extent of the territory is generally visited every 8-14 days. In the austral winter, indris will sometimes descend to lower levels of trees to avoid biting insects.
Indris can be sympatric with a number of other lemur species. For example, at Betampona Natural Reserve, they are sympatric with mouse lemurs (Microcebus sp.), greater dwarf lemurs (Cheirogaleus major), eastern fork-marked dwarf lemurs (Phaner furcifer), sportive lemurs (Lepilemur mustelinus), aye-ayes (Daubentonia madagascariensis), grey gentle lemurs (Hapalemur griseus), white-fronted lemurs (Eulemur albifrons), black-and-white ruffed lemurs (Varecia variegata), eastern avahis (Avahi laniger), and diademed sifakas (Propithecus diademed).