E. Geoffroy, 1796 after the Indri of Sonnerat, 1782 (Sonnerat pl88)
General characteristics
The genus Indri might have been used in synonym with the genera Indris G. Cuvier, 1800, Indrium Rafinesque, 1815, Lichanotes Temminck, 1827, Pithelemur Lesson, 1840.
The genus consist of only one species: Indri indri (Gmelin, 1788).
The indris are the most specialized, living representatives of the Indriidae. They are the largest of the extant Malagasy lemurs. Generally, the pelage is black and white colored. The tail is strongly reduced and measures only several centimeters.
In contrast to Propithecus, Indri has a small distribution. They live only in the northern part of the eastern forest. They live above all in mountainous zones where a constant humid climate prevails, where it is quite cold during the winter with temperatures only rarely surpassing 15 °C and often descending to around 0 °C.
They are cryptic animals, almost always difficult to observe, but they are well known by their melodious cries that can be heard from far away. Exceptions are zones like the Réserve d'Andasibe (Périnet) where the animals are accustomed to the presence of public. They can rapidly move by jumping from trunk to trunk and they live in small family groups of two to five or sometimes six individuals.
Until the last decade, many aspects of their biology still remained quite mysterious, which is essentially due to their conspicuous character and the uneven natural setting of their mountainous habitat. Studies in the field (Petter, 1962; Petter and Peyriéras, 1974 and especially Pollock, 1975) made it possible to fill some of the gaps.
Systematics
The museum specimens, examined by Petter, showed only little chromatic variation. At different places within the distribution of Indri indri, observations from several scientists and from Peyriéras (pers. comm.) made it possible to conclude that the animals living at Périnet are relatively brightly colored with an nearly beige back, whereas the animals living at Maroantsetra have a much duller coloration and those animals observed in an intermediate zone (Réserve naturelle intégrale no. 3, northeast of Tamatave) have a completely silvery back with very little white. However, all color forms can be grouped in the same species, because they only represent only shade differences found within probably all the intermediates.