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Census of Mountain Gorilla Population Shows Numbers Continue to Rise

Once on the brink of extinction, mountain gorillas continue to grow in number. Today, the Greater Virunga Transboundary Collaboration, a coalition of governments, non-profits and conservationists, announced the final results of a census of a population of mountain gorillas living in Uganda’s Bwindi Impenetrable National Park and the adjacent Sarambwe Reserve in DR Congo. The results show that the population there has increased to 459 individuals, from 400 at the last census. Including the mountain gorillas living in the Virunga mountain range of Rwanda and Congo, the overall total of mountain gorillas is now 1,063.

The Dian Fossey Gorilla Fund assisted the Bwindi survey. Dr. Tara Stoinski, president, CEO and chief scientific officer of the Fossey Fund, says, “Today’s census results are a testament to the intensive on-the-ground conservation efforts by dedicated trackers, researchers and other team members, and cooperation across three governments. Mountain gorillas are one of the most protected species on the planet, and today we see what a concerted effort by multiple stakeholders can do to reverse a seemingly hopeless situation. It takes hard work by community members, government leaders and conservationists—but it can be done.”

As in the previous mountain gorilla census, survey teams walked pre-determined reconnaissance trails covering all areas of the forest, searching for gorillas and other mammals as well as signs of human activity. Teams collected fecal samples for genetic analysis at nest sites. The process was completed twice, from March to May 2018 and from October to December 2018 to ensure no gorillas went undetected.

Team members collect feces at a nest site for genetic evaluation.
Photo: Winnie Eckardt

Survey teams also searched for signs of other mammals, such as elephants and chimpanzees.  There were no indications of declines in those populations since 2011.

Last year, a similar survey of the Virunga mountain gorilla population found an increase from 480 to 604 over a five-year period. Thirty years ago there were just 240 individuals left in the Virunga Mountains (with an unknown number in Bwindi), and this increase in numbers shows that years of effort on behalf of the mountain gorillas are truly making a difference, Stoinski says. The news was a cause for celebration in the conservation world, and the International Union for Conservation of Nature (IUCN) upgraded mountain gorillas’ endangered status from critically endangered to endangered.

While news of the Bwindi population increase is welcome, says Stoinski, the overall small numbers and other potential dangers such as disease, climate change and habitat encroachment mean that the survival of mountain gorillas is still at risk.

They have been pulled back from the brink of extinction due to what Dr. Stoinski calls “extreme conservation,” which focuses on daily protection of individual gorillas and their families. The increase in population “shows what can be accomplished by a cross-border, multipronged, unrelenting effort to protect a species,” she says, noting that gorillas “remain a conservation-dependent species and must be continually protected.”

The Bwindi population of gorillas is approximately 50 kilometers [30 miles] away from the mountain gorillas of the Virunga mountains that span Rwanda, Uganda and the Democratic Republic of Congo, where the Fossey Fund works. The Bwindi population was once even thought to constitute a separate subspecies, but subsequent genetic analyses showed that they are indeed mountain gorillas (Gorilla beringei beringei).

Team members at a nest site.
Photo: Winnie Eckardt

The Fossey Fund was one of many stakeholders offering support for the census, a painstaking headcount of gorillas living in Uganda’s Bwindi Impenetrable National Park and the adjacent Sarambwe Reserve in DR Congo, which was conducted by the Protected Area Authorities in Uganda and the Democratic Republic of Congo under the framework of the Greater Virunga Transboundary Collaboration. Other partners included the Rwanda Development Board, International Gorilla Conservation Programme, Mammalian Ecology and Conservation Unit of the UC Davis Veterinary Genetics Laboratory, Max Planck Institute for Evolutionary Anthropology, Institute of Tropical Forest Conservation, Gorilla Doctors, Conservation Through Public Health, Wildlife Conservation Society Uganda Country Office, WWF Uganda Country Office and Bwindi Mgahinga Conservation Trust. The census was funded by Fauna & Flora International, WWF and Partners in Conservation at the Columbus Zoo & Aquarium.

Felix Ndagijimana, director of the Fossey Fund’s Rwanda programs and Karisoke Research Center, calls the census “a great example of collaboration between governments, conservation organizations like the Fossey Fund and local communities.”

How the Bwindi Census was Done

The Bwindi census took place in two sweeps in 2018 and was the result of a large collaborative effort among national park authorities from all three countries where mountain gorillas are found as well as conservation NGOs. Trackers, researchers, veterinarians and others divided into 12 teams, with six in the forest at a time. These teams further divided into three groups, each of which camped in different parts of the forest for two weeks at a time, walking along pre-planned routes each day to search for signs of gorillas, especially nest sites, and collecting fecal samples for DNA analysis that would provide clear gorilla identification.

Fossey Fund trackers Prosper Kaberabose, Clement Tuyishime Kagaba, Olivier Hodari and Phocas Nkunzingoma participated, while Fossey Fund’s Rwanda research manager Dr. Winnie Eckardt served as a co-instructor for the teams in the initial training phase.

Team members practice ahead of the census start.
Photo: Winnie Eckardt

“The census outcome is only as accurate and reliable as the quality of data collected by the teams,” says Dr. Eckardt, explaining that the teams underwent an intensive five-day training, including theoretical and practical lessons, and learned how to use handheld electronic devices for more accurate data entry.
Prosper Kaberabose was one of the Fossey Fund trackers who worked in the census. “The census work is a tough job—physically demanding, with 12 hours each day of walking through the forest, crossing big ravines and climbing mountains,” he says. “But in addition to the conservation importance, it allowed the team members to increase their technical skills, such as collecting samples and using GPS, as well as to share and learn from staff from the three different countries and backgrounds. It was truly a collaborative effort.”