The indri is the largest living lemur, a black-and-white tree-dwelling primate found only in the rainforests along Madagascar's eastern escarpment [IUCN 2020] [ADW 2024]. It is best known for its loud, structured songs, which carry across the forest canopy and can last from roughly 45 seconds to more than three minutes [LCN 2023] [ADW 2024]. Among the world's primates it is one of the most imperiled, with a population that is small, severely fragmented, and declining [IUCN 2020].
Unlike most lemurs, the indri has only a rudimentary tail and moves through the forest as a vertical clinger and leaper, springing between trunks with its long, muscular hind legs [LCN 2023]. Its slow life history — late maturity and infrequent births — makes recovery from population loss especially difficult [LCN 2023] [IUCN 2020].
Biology and Identification
The indri has a head-and-body length of roughly 64–72 cm and weighs about 6–9.5 kg, making it, alongside the diademed sifaka, the largest extant lemur [ADW 2024] [LCN 2023]. Its dense coat is patterned in black and white, and its near-absent tail distinguishes it immediately from other large lemurs [LCN 2023].
It is diurnal and primarily folivorous, favoring young, tender leaves but also consuming flowers, fruit, seeds, and bark; it occasionally descends to ingest soil, a geophagic behavior thought to help process plant compounds [LCN 2023] [Borruso et al. 2021]. Indris live in small monogamous family groups of about two to six individuals, typically a mated pair and their offspring, within a female-dominant social structure characteristic of many lemurs [LCN 2023] [ADW 2024]. Family groups produce loud cooperative songs used in territorial spacing and group cohesion, often several times per day [LCN 2023].
Reproduction is notably slow. Females do not reach sexual maturity until about seven to nine years of age and give birth only once every two to three years, usually to a single infant [LCN 2023]. This low reproductive rate constrains how quickly depleted groups can rebuild [IUCN 2020].
Habitat and Range
The indri is endemic to Madagascar, restricted to lowland and montane rainforest along the island's eastern coast [IUCN 2020] [LCN 2023]. Its distribution runs from the Anjanaharibe-Sud Special Reserve in the north to forests near the southern limit of its range, with the overall population described as severely fragmented across this band of forest [IUCN 2020] [LCN 2023]. The species occurs in several protected areas, including the Analamazaotra and Anjanaharibe-Sud reserves and Zahamena National Park [LCN 2023].
Conservation Status
The indri is assessed as Critically Endangered on the IUCN Red List, in the assessment published in 2020 [IUCN 2020]. The total population is estimated at roughly 1,000–10,000 mature individuals, and the trend is decreasing; the assessment suspects a decline exceeding 80% over three generations (approximately 33 years), driven mainly by continuing habitat loss, hunting, and climate change [IUCN 2020]. The assessment notes the species remains under severe and compounding pressure across its restricted range [IUCN 2020].
Threats
The principal threat is the loss and fragmentation of eastern rainforest through slash-and-burn agriculture, logging, and fuelwood and charcoal gathering [IUCN 2020] [LCN 2023]. Madagascar has lost more than 90% of its original forest cover over the past two millennia, and deforestation rates in prime indri habitat increased by more than 1% per year between 2010 and 2014 [NEPC 2023].
Hunting is a second major pressure. Traditional fady (taboos) once shielded the indri from being killed in many communities, but the erosion of these customs — linked to social disruption following the 2009 political crisis and to in-migration of people without the same taboos — has been associated with increased hunting [LCN 2023] [IUCN 2020].
Climate change compounds these pressures. Modeling by Brown and Yoder projected that the indri's range could contract by about 39.5% between 2000 and 2080 from climate effects alone, while later modeling by Morelli and colleagues indicated that Madagascar's eastern rainforest habitat could be drastically reduced by 2070 under combined climate and deforestation scenarios [Brown & Yoder 2015] [Morelli et al. 2020].
What Is Being Done
Conservation work focuses on protecting and connecting remaining rainforest. The indri occurs within a network of national parks and special reserves that provide legal habitat protection [LCN 2023] [IUCN 2020], and the species is listed on CITES Appendix I, which prohibits commercial international trade [CITES 2024]. Field programs by Malagasy and international organizations combine habitat protection, reforestation, and community engagement; the indri has never been successfully maintained in long-term captivity, so in-situ forest conservation is the only viable path for the species [ADW 2024] [LCN 2023]. Research efforts, including studies of the species' gut microbiome and geophagy, aim to better understand its biology and the constraints on its persistence [Borruso et al. 2021].
How You Can Help
Because the indri exists only in Madagascar's eastern forests, the contributions most aligned with its persistence are supporting organizations that protect and restore those forests and that work alongside local communities on sustainable land use [LCN 2023]. Learning about and sharing accurate information on lemur conservation, and supporting reputable, transparent conservation programs working in the region, both contribute to efforts to keep remaining indri populations and their habitat intact [LCN 2023] [IUCN 2020].
References
[IUCN 2020] King, T., Patel, E., Rajaonson, A., Randrianarimanana, L., Ratsimbazafy, J., Razafindramanana, J., et al. (2020). Indri indri (Indri). The IUCN Red List of Threatened Species 2020: e.T10826A115565566. https://dx.doi.org/10.2305/IUCN.UK.2020-2.RLTS.T10826A115565566.en
[LCN 2023] Lemur Conservation Network. (2023). Lemur Fact Sheet: Indri. https://www.lemurconservationnetwork.org/learn/lemur-species-fact-sheets/indri/
[ADW 2024] Animal Diversity Web. (2024). Indri indri (indri). University of Michigan Museum of Zoology. https://animaldiversity.org/accounts/Indri_indri/
[NEPC 2023] New England Primate Conservancy. (2023). Indri, Indri indri. https://neprimateconservancy.org/indri/
[Brown & Yoder 2015] Brown, J. L., & Yoder, A. D. (2015). Shifting ranges and conservation challenges for lemurs in the face of climate change. Ecology and Evolution, 5(6), 1131–1142. https://doi.org/10.1002/ece3.1418
[Morelli et al. 2020] Morelli, T. L., Smith, A. B., Mancini, A. N., Balko, E. A., Borgerson, C., Dolch, R., et al. (2020). The fate of Madagascar's rainforest habitat. Nature Climate Change, 10, 89–96. https://doi.org/10.1038/s41558-019-0647-x
[Borruso et al. 2021] Borruso, L., Checcucci, A., Torti, V., Correa, F., Sandri, C., Luise, D., et al. (2021). Disentangling the Possible Drivers of Indri indri Microbiome: A Threatened Lemur Species of Madagascar. Frontiers in Microbiology, 12, 668274. https://doi.org/10.3389/fmicb.2021.668274
[CITES 2024] Convention on International Trade in Endangered Species of Wild Fauna and Flora. (2024). Appendices I, II and III. https://cites.org/eng/app/appendices.php