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Providing evidence to improve practice

Individual study: Extreme conservation leads to recovery of the Virunga mountain gorillas

Published source details

Robbins M.M., Gray M., Fawcett K.A., Nutter F.B., Uwingeli P., Mburanumwe I., Kagoda E., Basabose A., Stoinski T.S., Cranfield M.R. & Byamukama J. (2011) Extreme conservation leads to recovery of the Virunga mountain gorillas. PLoS ONE, 6


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Guard habituated primate groups to ensure their safety/well-being Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical moist montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that a mountain gorilla Gorilla beringei beringei population where individual animals were closely guarded against poachers alongside ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. Increased protection through the guarding of gorillas explained 60% of the difference in growth rates between this population (treatment) and a second, unguarded population in the same area (control). The remaining 40% were likely accounted for by veterinary interventions for snares, respiratory disease, and other life-threatening conditions. As part of an ecotourism- and research project, gorillas in the guarded population were habituated to human presence, where visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, spending only a limited amount of time with gorilla groups, ensuring that visitors/researchers were healthy, and disinfecting visitor’s/researcher’s clothes, boots etc. Dead gorillas were clinically examined. The study does not distinguish between the effects of the different interventions mentioned above.

Implement continuous health monitoring with permanent vet on site Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that a mountain gorilla Gorilla beringei beringei population that was continuously monitored by vets alongside ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. Veterinary treatment for snares, respiratory disease, and other life-threatening conditions explained up to 40% of the difference in growth rates between this population and another population in the same area, which did not receive veterinary care. The remaining 60% were likely due to increased protection against poachers. As part of an ecotourism- and research project, gorillas in the treatment population were habituated to human presence where visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, spending only limited amounts of time with gorillas, ensuring that visitors/researchers were healthy and disinfecting visitor’s/researcher’s clothes, boots etc. Dead gorillas were clinically examined. The study does not distinguish between the effects of the other interventions mentioned above

Regularly disinfect clothes, boots etc. Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that the habituated mountain gorilla Gorilla beringei beringei population that was regularly visited by tourists and researchers whose clothes were disinfected to avoid disease transmission along with other interventions, increased in size over time. Habituated gorillas that were regularly visited by researchers/tourists that adhere to strict hygiene rules (treatment) grew at a higher rate than unhabituated gorillas (control) (4.1% increase vs 0.7% decline/year). Overall, the habituated population increased by 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. Visitors/researchers were requested to wash their hands, wear clean clothes, and wash their shoes before entering the forest. As part of the ecotourism- and research programmes, gorillas were habituated to human presence, where visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, ensuring that visitors/researchers were healthy, and spending a limited amount of time with gorilla groups. The population was continuously monitored by vets and gorillas received medical treatment if necessary. When gorillas died, their cause of death was examined. The study only tests for the effect of veterinary interventions, but does not distinguish between the effects of the other interventions mentioned above.

Ensure that researchers/tourists are up-to-date with vaccinations and healthy Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that the mountain gorilla Gorilla beringei beringei population that was regularly visited by healthy tourists and researchers alongside ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. Visitors/researchers were asked to report if they were not feeling well and were not allowed to visit the gorillas if they felt sick. As part of the ecotourism- and research programmes, gorillas were habituated to human presence, where visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, spending only a limited amount of time with gorilla groups, disinfecting visitor’s/researcher’s clothes, boots etc. The population was continuously monitored by vets and individuals received medical treatment if necessary. When gorillas died, their cause of death was examined. The study only tests for the effect of veterinary interventions, but does not distinguish between the effects of the other interventions mentioned above.

Wear face-masks to avoid transmission of viral and bacterial diseases to primates Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical moist montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that the mountain gorilla Gorilla beringei beringei population that was regularly visited by tourists and researchers that wore face-masks to avoid disease transmission along with ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. All visitors/researchers were recommended to wear N95 masks (when available) or a surgical mask when visiting the gorillas. Gorillas were habituated to human presence as part of the ecotourism and research programmes and visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, spending only a limited amount of time with gorilla groups, ensuring that visitors/researchers were healthy, and disinfecting visitor’s/researcher’s clothes, boots etc. In addition, the population was continuously monitored by vets and gorillas received medical treatment if necessary. When gorillas died, their cause of death was clinically determined. The study does not distinguish between the effects of the different interventions mentioned above.

Limit time that researchers/tourists are allowed to spend with habituated animals Primate Conservation

A controlled before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that the mountain gorilla Gorilla beringei beringei population that was regularly visited by tourists and researchers that were restricted in the amount of time they were allowed to spend with them alongside ten other interventions, increased over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. One-hour visits were made to each gorilla group daily by tourists. Researchers typically spent no more than four hours with the research-habituated groups. As part of the ecotourism- and research programmes, gorillas were habituated to human presence, where visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, ensuring that visitors/researchers were healthy, disinfecting visitor’s/researcher’s clothes, boots etc. Gorillas were continuously monitored by vets and received medical treatment if necessary. When gorillas died, their cause of death was clinically determined. The study does not distinguish between the effects of the different interventions mentioned above.

Prohibit (livestock) farmers from entering protected areas Primate Conservation

A before-and-after trial in 1967-2008 in tropical forest in Volcanoes, Mgahinga and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo, respectively (2) found that despite the removal of livestock from the park, along with other interventions, the mountain gorilla Gorilla beringei beringei population decreased over time. Annual population decline was 0.7%, resulting in an overall population decrease of 29% over 31 years. However, no statistical tests were carried out to determine whether this trend was significant or due to natural population fluctuations. Any cattle found by rangers were herded out of the park, confiscated, and their owners fined. Rangers also conducted regular anti-poaching patrols and regularly removed snares. Additional interventions included local conservation education and community development projects. The study does not distinguish between the effects of the different interventions mentioned above.

Regularly de-activate/remove ground snares Primate Conservation

A before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks located in Rwanda, Uganda, and the Democratic Republic of Congo, respectively, found that despite the regular removal of snares alongside other interventions, the mountain gorilla Gorilla beringei beringei population decreased over time. Annual population decline was 0.7%, resulting in an overall population decrease of 28.7% over the entire study period. However, no statistical tests were carried out to determine whether this decrease was significant. Rangers patrolled the whole park and confiscated more than 1,500 snares/year. They also conducted regular anti-poaching patrols and when necessary, herded livestock out of the park. Additional interventions included local conservation education and community development projects. The study does not distinguish between the effects of the different interventions mentioned above.

Habituate primates to human presence to reduce stress from tourists/researchers etc. Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical moist montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo, respectively, found that a mountain gorilla Gorilla beringei beringei population that was habituated to the presence of researchers and tourists alongside 10 other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over the entire study period. No statistical tests were carried out to determine whether this increase was significant. As part of a long-term research project, habituation of gorilla groups started in 1967 and continued largely uninterrupted until the end of the study in 2008. Later on, an ecotourism project was implemented. Visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, spending only a limited amount of time with gorilla groups, ensuring that visitors/researchers were healthy and disinfecting visitor’s/researcher’s clothes, boots etc. The population was monitored by vets and gorillas received medical treatment if necessary and any mortality was clinically examined. The study does not distinguish between the effects of the different interventions mentioned above.

Involve local community in primate research and conservation management Primate Conservation

A before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks located in Rwanda, Uganda, and the Democratic Republic of Congo, respectively, found that despite the implementation of an environmental education programme in local communities along with other interventions, the mountain gorilla Gorilla beringei beringei population decreased over time. Annual population decline was 0.7%, resulting in an overall population decrease of 28.7% over 31 years. However, no statistical tests were carried out to determine whether this difference was significant. Details on the local conservation education programme were not provided in the study. Additional interventions included regular anti-poaching patrols, the removal of snares and when necessary, the herding of live-stock out of the park, and the implementation of development projects in nearby communities. The study does not distinguish between the effects of the different interventions mentioned above.

Keep safety distance to habituated animals Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo (3) found that the mountain gorilla Gorilla beringei beringei population that was regularly visited by tourists and researchers which kept a safety distance to the animals along with ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. All visitors/researchers were expected to maintain a 7 m distance from the gorillas. As part of the ecotourism- and research programmes, gorillas were habituated to human presence, where visitors/researchers had to follow strict health procedures; these included wearing face-masks, spending only limited amounts of time with gorillas, ensuring that visitors/researchers were healthy, disinfecting visitor’s/researcher’s clothes, boots etc. Gorillas were continuously monitored by vets and received medical treatment if necessary. When gorillas died, their cause of death was clinically determined. The study does not distinguish between the effects of the different interventions mentioned above.

Provide monetary benefits to local communities for sustainably managing their forest and its wildlife (e.g. REDD, employment) Primate Conservation

A before-and-after study in 1967-2008 in tropical moist montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks located in Rwanda, Uganda, and the Democratic Republic of Congo, found that despite the implementation of development projects in nearby communities along with other interventions, the mountain gorilla Gorilla beringei beringei population decreased over time. Annual population decline was 0.7%, resulting in an overall population decrease of 28.7% over 41 years. However, no statistical tests were carried out to determine whether this decrease was significant. Development was promoted through providing local employment in the ecotourism sector. Additional interventions included regular anti-poaching patrols, the removal of snares and when necessary, the herding of live-stock out of the park, and the implementation of a local conservation education program. The study does not distinguish between the effects of the different interventions mentioned above.

Detect & report dead primates and clinically determine their cause of death to avoid disease transmission Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical moist montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo, respectively found that a mountain gorilla Gorilla beringei beringei population increased in size over time, when dead individuals were examined and their cause of death investigated alongside ten other interventions,. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this difference was significant. When a gorilla death was detected, the cause of death was clinically determined by an on-site vet. The population was continuously monitored by vets and individuals received medical treatment if necessary. As part of an ecotourism- and research project, gorillas were habituated to human presence, where visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, spending only a limited amount of time with gorillas, ensuring that visitors/researchers were healthy, and disinfecting visitors’/ researchers’ clothes, boots etc. The study does not distinguish between the effects of the other interventions mentioned above.

Conduct regular anti-poaching patrols Primate Conservation

A before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks located in Rwanda, Uganda, and the Democratic Republic of Congo, respectively, found that despite regular anti-poaching patrols along with other interventions, the mountain gorilla Gorilla beringei beringei population decreased over time. Annual population decline was 0.7%, resulting in an overall population decrease of 28.7% over the entire study period. No statistical tests were carried out to determine whether this decrease was significant. Anti-poaching patrols were carried out throughout the entire study area. Rangers mostly used established trails, but made their own trails if signs of poaching were observed and followed these signs until they located the illegal activity. Patrol teams also regularly removed snares and herded live-stock out of the park. Additional interventions included local conservation education and community development projects. The study does not distinguish between the effects of the different interventions mentioned above.

(Summarised by JJ)

Run tourist projects and ensure permanent human presence at site Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo, respectively found that a mountain gorilla Gorilla beringei beringei population that was part of an ecotourism program along with ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. As part of this program, gorillas were habituated to human presence. A long-term research program started in 1967. Visitors/researchers had to follow strict health procedures, included keeping a safety distance to the gorillas, wearing face-masks, spending only a limited amount of time with gorilla groups, ensuring that visitors/researchers were healthy, and disinfecting visitor’s/researcher’s clothes, boots etc. Gorillas were continuously monitored by vets and treated if necessary. When gorillas in the treatment population died, their cause of death was investigated. The study only tests for the effect of veterinary interventions, but does not distinguish between the effects of the other interventions mentioned above.

Run research project and ensure permanent human presence at site Primate Conservation

A controlled, before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo, respectively found that a mountain gorilla Gorilla beringei beringei population that was continuously monitored by researchers alongside ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% in 41 years. No statistical tests were carried out to determine whether this increase was significant. Gorillas were habituated to human presence and monitored by researchers for four hours during mid-day. An ecotourism project was subsequently implemented. Visitors/researchers followed strict health procedures, included keeping a safety distance to the gorillas, wearing face-masks, spending only a limited amount of time with gorilla groups, ensuring that visitors/researchers were healthy, and disinfecting visitor’s/researcher’s clothes, boots etc. The population was continuously monitored by vets and individuals were treated if necessary. Dead gorillas in the treatment population were examined and the cause for their death determined. The study only tests for the effect of veterinary interventions, but does not distinguish between the effects of the other interventions mentioned above.

Treat sick/injured animals Primate Conservation

A study in 1967-2008 in tropical moist montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo, found that the majority of the mountain gorillas Gorilla beringei beringei treated for snare wounds and respiratory disease along with 14 other interventions, survived for at least 41 years. The veterinary programme started in 1986. The snare wounds of 42 habituated gorillas were treated by veterinarians. Forty-one of the 42 (98%) treated gorillas survived for at least 41 years. Furthermore, 36 (86%) of 42 gorillas that treated for respiratory disease, recovered. Only animals showing severe clinical signs of respiratory disease for several consecutive days were treated. Veterinary interventions were performed on severely ill gorillas only after careful consideration of the disease course, and the potential disruption to the gorilla group from the darting. The study included no specific information on when each gorilla was treated and there was therefore no information on how long gorillas survived after individual treatment.