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FREQUENTLY ASKED QUESTIONS ON MOUNTAIN GORILLA CENSUS
1. What is a mountain gorilla census?
A mountain gorilla census is a population survey used to determine the number of
individual mountain gorillas within a defined area. The population survey for mountain
gorillas is so intensive that it is commonly referred to as a census.
2. Why and how often is the gorilla census done?
While births and deaths are known and recorded for those mountain gorilla groups that
are habituated to the presence of humans for either research or tourism, it is only during a
complete survey or census that we know whether the population as a whole - both
habituated and unhabituated gorillas - is stable, increasing or decreasing.
The census also provides vital information as to the demographics (age classes and sex
ratios) and number and size of family groups. The spatial data from nest sites also gives
scientists a snapshot of where groups are located in relation to vegetation types and in
relation to other gorilla groups and park boundaries and human activities.
Illegal activities encountered and signs of other key large mammals, like elephants, are
also recorded for analyses and interpretation.
Each population of mountain gorillas is surveyed every five years if conditions are
conducive and human and financial resources are available.
3. How is gorilla census conducted?
The actual field work involves teams of people hiking through the forest – essentially
combing the forest in search of gorilla trails and nest sites. They then collect gorilla
faecal samples from every nest they encounter. Those samples are delivered to our
partners at Max Planck Institute for Evolutionary Anthropology, who analyze each
sample for individual DNA identifiers to ensure that each individual gorilla is counted
only once.
To facilitate thorough coverage of the entire Virunga Massif, the area is divided and
mapped into sectors. The field teams cover the entire Virunga Massif sector by sector.
They walk reconnaissance trails that are spaced no further than 500 m apart. A complete
survey of all the sectors is called a “sweep.” For this census, it is planned that two sweeps
will be conducted to allow for scientists to estimate the detection probability for each
effort, and more accurately estimate the total population.
4. Who is involved in the 2015 Virunga Massif mountain gorilla census?
The Virunga Massif mountain gorilla census is being conducted by the Protected Area
Authorities in the DRC, Rwanda, and Uganda (l’Institut Congolais pour la Conservation
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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 Fauna & Flora International and WWF), Max Planck Institute for
Evolutionary Anthropology, Dian Fossey Gorilla Fund International, Institute of Tropical
Forest Conservation, Gorilla Doctors, and North Carolina Zoo.
The census is funded through generous contributions from Fauna & Flora International,
WWF, and Partners in Conservation at the Columbus Zoo & Aquarium.
5. How is security of the teams ensured?
Teams will be accompanied by park rangers at all times throughout the exercise. In
addition, the Park Authorities are working closely with security forces within the three
States. This cooperation in the transboundary context is made possible through the
Greater Virunga Transboundary Collaboration.
6. When was the last gorilla census and what were the findings?
Mountain gorillas exist in two isolated populations – one in the Virunga Massif and one
in Uganda’s Bwindi Impenetrable National Park contiguous with DRC’s Sarambwe
Nature Reserve.
The last census within the Virunga Massif was conducted in 2010 and resulted a
population estimate of 480 individual gorillas in 36 groups as well as 14 lone silverbacks
(solitary mature males).
The last census within Bwindi Impenetrable National Park was conducted in 2011 and
resulted in a population estimate of 400 individual gorillas in 36 social groups and 16
lone silverbacks.
7. What is the gorilla population trend, is it increasing, decreasing or stable?
Both populations of mountain gorillas are demonstrating positive growth in population
over the last two decades (see graphs below). It is important to note that techniques for
detecting individual mountain gorillas and verifying each unique individual have been
improving over time, making population estimates for these rare and elusive animals
more accurate for each consecutive census.
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8. What are some of the challenges encountered during gorilla census and how are
they over come?
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The rugged terrain of the Virunga Massif will be a challenge to teams and their
movement through the area with steep slopes shrouded in dense Afromontane forest with
many ravines.
The census requires a high level of coordination by multiple agencies and institutions.
The logistics of rotating groups of teams in and out of the forest sometimes in remote
camps on two week cycles so that the census can continue while allowing one group to
rest while another continues with data collection. In addition, the logistics to keep the
teams supplied with water, food, and power is a challenge.
The census is also conducted in a complex cultural landscape where there is no single
dominant language and the teams communicate in a mix of English, French, Kiswahili,
and Kinyarwanda/Kinyabwisha/Kifumbira.
9. What is different in the upcoming census that wasn’t done in the previous counts of
the mountain gorilla?
For the first time, this census will make use of electronic devices for information and data
entry by the teams in the field. The use of this new technology is expected to allow for
more streamlined data collection and eliminate manual data entry. The census will also
build on past advancements in terms of genetic analyses and mark recapture mathematics.
In addition, an effort to establish a DNA library for the known individual gorillas from
habituated groups will serve as a reference point to the collected samples to reduce the
potential to double-count individuals or under-count the overall population.
Photos are available here:
https://www.dropbox.com/sh/vl8qjy17xtaz0jp/AACm-9i3QdVic35RSAlLLp_Ca?dl=0
The photos should be credited to the organization indicated in the photo file name.