Updated
Scientists count mountain gorillas with periodic censuses that combine field surveys and DNA. Teams walk systematic routes through the whole forest, recording fresh nests and trails, and collect dung from nest sites so genetic analysis can tell individual gorillas apart and avoid double counting. The most recent full counts found about 459 gorillas in Bwindi and Sarambwe in 2018 and 604 in the Virunga Massif in 2015 to 2016, giving a total of just over 1,000.
How a census works
Teams sweep the forest in parallel lines, following trails to night nest sites, where they count nests by size to estimate group composition. Dung samples are analysed in laboratories to identify individuals. Habituated groups, which are monitored daily, are counted directly. The results show group sizes, age structure and how many gorillas live in unhabituated groups.
Daily monitoring
Between censuses, trackers record the health, births, deaths and movements of every habituated family, and rangers note signs of other groups. Camera traps and patrol data add information. This monitoring lets vets spot illness early and helps managers measure the effect of tourism and protection.
Why it matters
Mountain gorillas are the only great ape whose numbers have been rising, which led to their move from Critically Endangered to Endangered in 2018. The gorilla permit costs US$800, or US$600 in April, May and November. See our guides to how many mountain gorillas are left, camera traps, nose prints and Gorilla Doctors.
Frequently asked questions
With forest-wide surveys of nests and trails, plus DNA from dung to identify individuals.
Just over 1,000, based on the latest censuses.
About 459 were counted in Bwindi and Sarambwe in 2018.
To tell individuals apart and avoid counting the same gorilla twice.
