Gorillas are endangered because of a combination of habitat destruction, disease, poaching, armed conflict, and a reproductive rate too slow to bounce back quickly from population losses. All four subspecies face serious threats, with western lowland gorillas and Cross River gorillas classified as critically endangered. Mountain gorillas, the subspecies most people picture when they think of silverbacks, have seen their numbers climb from fewer than 400 in the early 1980s to an estimated 1,063 today, but they remain vulnerable to many of the same pressures.
How Many Gorillas Are Left
The western lowland gorilla is the most numerous subspecies, with a 2013 range-wide estimate of roughly 362,000 individuals. That sounds like a large number, but the population has been declining rapidly due to Ebola outbreaks and deforestation. Both the western lowland gorilla and the Cross River gorilla are listed as critically endangered on the IUCN Red List.
Mountain gorillas were downgraded from critically endangered to endangered in 2018 after decades of conservation work pushed their numbers upward. The current count of about 1,063 individuals, split between Uganda, Rwanda, and the Democratic Republic of Congo, represents a genuine success story. But a population of roughly a thousand animals confined to two small mountain ranges is still precarious. Eastern lowland (Grauer’s) gorillas have experienced steep declines as well, driven largely by mining and civil conflict in eastern Congo.
Habitat Loss From Industry and Agriculture
Logging and mining operations are the largest drivers of gorilla habitat destruction across Central Africa. Companies clear forest to extract timber, coltan (used in electronics), gold, and other minerals. Smallholder farming also pushes into gorilla territory as human populations grow. The Congo Basin, which contains the vast majority of gorilla habitat, loses forest cover every year to a mix of industrial and agricultural expansion.
For mountain gorillas specifically, the problem is geography. They live at high elevations in a narrow band of montane forest, and the land surrounding their habitat is some of the most densely populated rural territory in Africa. There is very little room for their range to expand, and the forests they depend on are bordered by farmland on nearly every side.
Ebola and Human Diseases
Ebola virus has been catastrophic for gorillas. Estimated mortality rates of up to 98% in affected groups have reduced the global gorilla population by roughly one-third. At study sites near human Ebola outbreak zones, western lowland gorilla populations declined by 56 to 98%. Modeling suggests that without vaccination, Ebola spreads through gorilla groups rapidly, eventually infecting 85 to 87% of individuals. Only about 6% of infected gorillas recover.
Ebola is not the only disease threat. Human respiratory viruses, including respiratory syncytial virus and metapneumovirus, have been detected in both mountain gorillas and western lowland gorillas during respiratory outbreaks. Because gorillas share about 98% of human DNA, they are highly susceptible to our pathogens. Tourism and research, while critical for conservation funding, bring humans into close contact with gorilla groups and create opportunities for disease transmission. A single respiratory illness introduced by a visitor or researcher can sweep through an entire troop.
Armed Conflict in Gorilla Territory
Virunga National Park in the Democratic Republic of Congo, home to a significant portion of the world’s mountain gorillas, sits in one of the most volatile conflict zones on the planet. More than 150 park rangers have been killed in the line of duty since 1996. Armed groups, including M23 rebels and various militia factions, have fought in and around the park for over two decades, and the underlying driver of much of this conflict is the illegal exploitation of natural resources found within park boundaries.
When fighting intensifies, rangers sometimes cannot monitor gorilla populations for months at a time. Gorillas do not flee from gunfire the way other animals might. They tend to stay in their home range, which puts them directly at risk. Some gorillas have been killed in crossfire during Congo’s civil wars. Beyond direct violence, conflict disrupts anti-poaching patrols, damages infrastructure, and displaces local communities into forested areas where they may hunt bushmeat or clear land for shelter.
Slow Reproduction Makes Recovery Difficult
Even when threats are reduced, gorilla populations recover slowly. Females have a gestation period of about 255 days (roughly eight and a half months), and they typically produce a single infant. The interval between births is long because mothers nurse for several years before they are ready to conceive again. This means a female gorilla may produce only a handful of surviving offspring in her lifetime.
The social structure of gorilla groups adds another layer of vulnerability. A silverback, the dominant adult male, is the protector of his group. When a silverback dies, the group can fragment, and infants become targets for infanticide by outside males seeking to take over. Research spanning more than 40 years of data from mountain gorillas found that infanticide accounted for up to 21% of all infant mortality and up to 5.5% of offspring born during the study period. Groups with only one adult male are especially at risk if that male is killed by poachers or caught in conflict.
Genetic Vulnerability From Small Populations
Decades of population decline have left eastern gorillas, particularly mountain gorillas, with dangerously low genetic diversity. Genome sequencing has revealed that mountain gorillas are typically identical across both copies of their chromosomes for about 34% of their DNA, a level of inbreeding that exceeds even the most inbred human populations and surpasses what has been observed in ancient Neanderthal remains. The very long stretches of identical DNA in mountain gorillas suggest several recent generations of mating between close relatives, equivalent to pairings between half-siblings.
Eastern gorillas have two to three times less genetic diversity than their western lowland relatives. Their mitochondrial DNA (passed from mother to offspring) shows almost no variation at all, with only three distinct types found across the entire mountain gorilla population, differing by just one to three mutations. The effective population size, a measure of how many individuals are actually contributing genes to the next generation, is estimated at only about 273 for mountain gorillas. Low genetic diversity makes a population more susceptible to disease, less adaptable to environmental change, and more likely to accumulate harmful genetic mutations over time.
Climate Change and Shrinking Habitat
Climate projections for sub-Saharan Africa predict a temperature increase of 3.6°C and longer dry seasons by 2090, with rainfall becoming less evenly distributed throughout the year. For mountain gorillas, this could shift plant communities upward by 600 to 700 meters in elevation. Since mountain gorillas already live near the tops of volcanic ranges, there may simply be no higher ground for their food plants to move into.
Warmer, longer dry seasons combined with more concentrated rainfall reduce overall plant growth, which could shrink the food supply gorillas depend on. Mountain gorillas eat large quantities of leaves, stems, and bark from specific plant species. If those plants shift in distribution, decline in abundance, or change their fruiting and leafing schedules, gorillas will face increased competition for food within their already limited range.
Why Conservation Has Worked for Mountain Gorillas
The increase from fewer than 400 mountain gorillas in the 1980s to over 1,000 today did not happen by accident. It required coordinated effort among three national governments, dozens of conservation organizations, and local communities. Revenue-sharing from gorilla tourism gave communities around the parks a financial stake in protecting the animals. Veterinary teams began intervening when gorillas were caught in snares or showed signs of illness. Ranger patrols, despite extraordinary danger, maintained a continuous presence in gorilla habitat.
This progress is real but fragile. The total population of mountain gorillas still fits inside a single large building. A single Ebola outbreak, a new wave of armed conflict, or a sustained loss of habitat could reverse decades of gains. Western lowland gorillas, despite numbering in the hundreds of thousands, face even steeper percentage declines because the threats across their much larger range are harder to monitor and control. For all gorilla subspecies, the margin between recovery and collapse remains thin.