The largest ape, Grauer's gorilla Gorilla beringei graueri, is only found in the east of the Democratic Republic of Congo (DRC). The civil war in DRC that started in 1996 and ended in 2003 led to political destabilization in the east and the creation of many militia. These armed groups engaged in artisanal mining to fund their operations, extorted money from the local population, and hunted bushmeat at remote mining camps, leading to declines in large mammal species around these camps. In 1994, prior to the civil war, Grauer's gorilla was estimated to number c. 17,000 individuals. In joint work the Wildlife Conservation Society, Fauna & Flora International and Institut Congolais pour la Conservation de la Nature surveyed this ape across its range during 2011–2015. The results demonstrate that where there is comparative census data to the surveys made in 1994, the number of gorillas has declined by 87%. Encounter rate data of gorilla nests at 11 sites across the subspecies' range also indicate declines of 85–96% at seven of the 11 sites; at the other sites declines have been less marked (5–10% at three sites and an increase of 40% at one site where protection is good). Spatial occupancy analysis identified the Kahuzi-Biega National Park and adjacent Reserve des Gorilles de Punia, together with the remote and previously undocumented Usala Forest, as the most critical sites for the remaining populations of this ape. An estimated 2,585 (95% CI 1,802–4,528) Grauer's gorillas remain across their range. These results indicate that Grauer's gorilla should be recategorized from Endangered to Critically Endangered on the IUCN Red List. For further details, see www.albertinerift.org.