The vaquita porpoise, with fewer than 10 individuals remaining in the wild, is the world's most endangered mammal — a victim of illegal gillnet fishing in Mexico's Gulf of California.
The International Union for Conservation of Nature (IUCN) Red List classifies species into categories of extinction risk based on population size, rate of decline, geographic range, and other factors. The species on this list all hold the highest threat classification — Critically Endangered — and represent the mammals closest to extinction in the wild.
This list ranks the ten most endangered mammal species by their estimated remaining wild adult population, from smallest to largest. Data comes from the IUCN Red List assessments, which are the global standard for conservation status. The rankings reflect the most recent published estimates, which in some cases are several years old due to the difficulty of surveying extremely rare species.
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Estimated wild population (mature individuals)
Estimated wild population (mature individuals)
Vaquita
Javan Rhino
Hainan Gibbon
Amur Leopard
Sumatran Rhino
Saola
Cross River Gorilla
Mountain Gorilla
Pangolin (Sunda pangolin)
African Forest Elephant
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The ranking
1
Vaquita
The world's smallest porpoise and most endangered marine mammal, the vaquita is found only in the northern Gulf of California, Mexico. The population has collapsed from an estimated 567 individuals in 1997 to fewer than 10 today, driven almost entirely by entanglement in illegal gillnets set for the totoaba fish, whose swim bladder is highly valued in traditional Chinese medicine.
scientificName: Phocoena sinustype: Porpoiserange: Gulf of California, MexicoprimaryThreat: Gillnet bycatch
2
Javan Rhino
The Javan rhinoceros survives in a single population within Ujung Kulon National Park on the western tip of Java, Indonesia. Once widespread across Southeast Asia, it was driven to the brink by poaching for its horn. The remaining population is critically vulnerable to disease, natural disasters, and inbreeding depression.
scientificName: Rhinoceros sondaicustype: Rhinocerosrange: Ujung Kulon NP, Java, IndonesiaprimaryThreat: Poaching, habitat loss
3
Hainan Gibbon
The world's rarest primate, the Hainan gibbon is found only in Bawangling National Nature Reserve on Hainan Island, China. The population crashed from an estimated 2,000 individuals in the 1950s to fewer than 10 by the 2000s, driven by habitat loss and hunting. It has since stabilized at roughly 37 individuals across 5 family groups.
The world's rarest big cat, the Amur (or Far Eastern) leopard survives in the temperate forests of the Russian Far East and adjacent areas of China. Its population has slowly recovered from a low of around 30 individuals in 2007 to an estimated 120 today, thanks to intensive anti-poaching patrols and habitat protection programs.
scientificName: Panthera pardus orientalistype: Big catrange: Russian Far East, northeastern ChinaprimaryThreat: Poaching, habitat fragmentation
5
Sumatran Rhino
The smallest and hairiest of the living rhinoceros species, the Sumatran rhino once ranged across Southeast Asia. Fewer than 80 individuals remain in fragmented populations on Sumatra and Borneo. The species has been functionally extinct in the wild in Malaysia since 2019, and captive breeding efforts have had limited success.
Often called the 'Asian unicorn,' the saola is one of the rarest large mammals on Earth. Discovered by science only in 1992 in the Annamite Mountains of Vietnam and Laos, it has never been photographed in the wild by a scientist more than a handful of times. Population estimates are highly uncertain but suggest fewer than 100 mature individuals remain.
scientificName: Pseudoryx nghetinhensistype: Bovid (forest ungulate)range: Annamite Mountains, Vietnam and LaosprimaryThreat: Hunting (snaring), habitat loss
7
Cross River Gorilla
The most endangered African ape, the Cross River gorilla survives in a dozen fragmented populations along the Nigeria–Cameroon border. Camera-trap surveys estimate fewer than 300 mature individuals remain. Unlike mountain gorillas, which have recovered through intensive conservation, Cross River gorillas have received far less attention and funding.
scientificName: Gorilla gorilla diehlitype: Great aperange: Nigeria–Cameroon border regionprimaryThreat: Hunting, habitat loss
8
Mountain Gorilla
Through decades of intensive conservation, the mountain gorilla population has grown from a low of approximately 254 individuals in the 1980s to an estimated 1,063 mature individuals today. The entire population lives in just three national parks spanning Rwanda, Uganda, and the Democratic Republic of Congo, making it highly vulnerable to disease and conflict.
All eight species of pangolin are protected under CITES Appendix I, but the Sunda pangolin is the most threatened of the Asian species. It is the most trafficked mammal in the world due to demand for its scales in traditional medicine and its meat as a luxury food. Wild population estimates are highly uncertain, with fewer than 5,000 mature individuals thought to remain.
scientificName: Manis javanicatype: Pangolinrange: Southeast Asia (Thailand, Malaysia, Indonesia, Vietnam)primaryThreat: Illegal wildlife trafficking
10
African Forest Elephant
The African forest elephant was reclassified as a separate species from the savanna elephant in 2021 and assessed as Critically Endangered. Its population has declined by an estimated 86% over 31 years due to poaching for ivory and habitat loss. The most recent continent-wide survey estimated fewer than 20,000 mature individuals remain in the dense central African rainforests.
scientificName: Loxodonta cyclotistype: Elephantrange: Central and West African rainforestsprimaryThreat: Ivory poaching, habitat loss
Southeast Asia (Thailand, Malaysia, Indonesia, Vietnam)
Illegal wildlife trafficking
10
African Forest Elephant
Loxodonta cyclotis
Elephant
Central and West African rainforests
Ivory poaching, habitat loss
How we ranked this
Species are ranked by estimated number of mature individuals remaining in the wild, from lowest (rank 1 — most endangered) to highest. Only mammals classified as Critically Endangered by the IUCN Red List are considered. Population figures are drawn from the IUCN Red List's most recent published species assessments and supplemented by peer-reviewed conservation surveys published in journals such as Oryx and Conservation Biology. Species with zero known wild individuals (extinct in the wild) are excluded. Figures are estimates and may carry wide confidence intervals due to the difficulty of surveying rare and elusive animals.
FAQ
What does 'mature individuals' mean in population estimates?
The IUCN defines 'mature individuals' as individuals known, estimated, or inferred to be capable of reproduction. This excludes juveniles, dependent offspring, and senescent individuals past breeding age. It is the standard metric used in Red List assessments because it reflects the effective breeding population.
Why are some well-known endangered species not on this list?
Several well-known species — such as giant pandas, snow leopards, and Bengal tigers — are classified as Vulnerable or Endangered rather than Critically Endangered, meaning their wild populations are larger than the species on this list. Giant pandas, for example, have an estimated population of over 1,800 in the wild.
How reliable are these population estimates?
Population estimates for rare and cryptic species carry significant uncertainty. The vaquita estimates are based on acoustic monitoring and visual surveys with narrow confidence intervals, while estimates for species like the Sunda pangolin are broad approximations. The figures presented here are the best available scientific estimates from the IUCN Red List and peer-reviewed surveys.
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