Counting Our Blessings, Not Once But Twice: Planning underway for the next count of mountain gorillas in the Virunga Massif

Although the term census was historically used to describe periodic population estimates of mountain gorillas, Dr. Jena R. Hickey, a population ecologist and the IGCP Conservation Scientist, prefers to call it a survey. According to Jena ‘census’ implies that all members are counted, yet in wildlife populations, one can never be sure that every single individual in the target community has been found. “I prefer to refer to it as a population survey, and to state the results as an approximate range or confidence interval, because it is not possible to know if you’ve found and counted every individual in the population,” Jena asserts.

Jena points out that a good scientist is aware of and acknowledges what they do not know as much as what they do know. She appreciates that not every individual is likely to be found in the upcoming gorilla census; although she explains that the DNA-mark-recapture method to be used will allow the scientific team to estimate the detection probability – that is – not just how many gorillas were found, but also how many were probably missed during the survey. This combination will provide a robust population estimate.

Typically with other wildlife species, mark-recapture refers to capturing individuals and tagging each with a unique identification label. However, in the survey of mountain gorillas, no individuals are captured or tagged, instead DNA that is found in gorilla fecal droppings is analyzed to individual. Like a fingerprint, the DNA helps the researchers identify which individual deposited each dropping. Then, the survey is conducted twice in the same area: the first survey occasion or “sweep” establishes a minimum number of individuals, whereas the second sweep is needed to approximate the number of individuals that were missed (not detected).

Last conducted in 2010, IGCP is supporting the Greater Virunga Transboundary Collaboration (GVTC) in planning another population survey in the near future of the mountain gorillas in the Virunga Massif. The primary purpose of this exercise is to estimate the number of mountain gorillas throughout the three National Parks forming the transboundary Virunga Massif with the associated objective to understand whether the population is increasing, decreasing or stable. Additional objectives of this effort include collecting data on illegal activities in the park, analyzing their relationship with gorilla population trends, and strengthening transboundary relationships between conservation institutions across the three countries – the Democratic Republic of the Congo, Rwanda, and Uganda.

The census as currently being planned is going to be conducted by over sixty (60) staff members from Uganda Wildlife Authority, Institut Congolais pour la Conservation de la Nature, Rwanda Development Board, Dian Fossey Gorilla Fund International, Gorilla Doctors, Institute of Tropical Forest Conservation, Max Planck Institute for Evolutionary Anthropology, and the International Gorilla Conservation Programme and at least ten (10) members of the community as porters and cooks. The North Carolina Zoo is providing technical support on the application of electronic data collection.

In preparation for the task ahead, the technical team was initially trained in March 2015 on how to use hand-held electronic devices, data entry and how to conduct the survey. In addition, the training covered map and compass use, planning the daily survey routes and ensuring thorough coverage of the entire Massif. The five-day training was held in Musanze District, Rwanda.

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Representatives from participating institutions testing the hand held devices in the field.

The participants were equipped with high quality protective rain gear (pants, jackets, gum boots) daypacks, and other navigation equipment, such as GPS units. Jena reveals that for the first time ever the census will be conducted using hand-held electronic devices for data collection. “It is a huge step forward in terms of efficiency both in the field and in office because it makes data collection easier – there is no more need for pen and paper in the rain – and data is downloaded directly from device to computer. This reduces staff time by eliminating data entry from field notebooks to computers and minimizes errors.” Some of the expected outcomes from this survey include establishing the locations and types of illegal activities in the park and their impact on the gorilla population, establishing the location of certain species of large mammals, and of course, establishing the current gorilla population estimate. Jena comments on the challenges encountered by teams during census field work saying, “just imagine the steep, muddy, terrain, covered in dense forest and coupled with rainy, cold weather – these teams endure a lot for the good of gorilla conservation.”

She looks forward to implementing the census with both hope and excitement about its results and their impact. “Even simply organizing the census has already been a fantastic success as we see all the conservation institutions collaborate as a unified team; it is a gigantic task, logistically and technically. I hope the census contributes to our understanding of mountain gorilla population trends, helps build the capacity of partner institutions, and results in a scientifically robust population estimate. I would be thrilled if the census is able to contribute in some way to improved transboundary relations,” says Jena.


The Virunga Massif mountain gorilla census is being conducted by the Protected Area Authorities in the Democratic Republic of Congo, Rwanda, and Uganda (l’Institut Congolais pour la Conservation de la Nature, the Rwanda Development Board and the Uganda Wildlife Authority) under the transboundary framework of the Greater Virunga Transboundary Collaboration. The census is supported by the International Gorilla Conservation Programme (a coalition of the Fauna & Flora International and WWF), the Max Planck Institute for Evolutionary Anthropology, the Dian Fossey Gorilla Fund – International, the Institute of Tropical Forest Conservation, Gorilla Doctors, and the North Carolina Zoo. Current funding for the census is through generous contributions from Fauna & Flora International, WWF, and Partners in Conservation at the Columbus Zoo & Aquarium.

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