Providing evidence to improve practice

Individual study: Assessing Initial Reintroduction Success in Long-Lived Primates by Quantifying Survival, Reproduction, and Dispersal Parameters: Western Lowland Gorillas (Gorilla gorilla gorilla) in Congo and Gabon

Published source details

King T., Chamberlan C. & Courage A. (2012) Assessing Initial Reintroduction Success in Long-Lived Primates by Quantifying Survival, Reproduction, and Dispersal Parameters: Western Lowland Gorillas (Gorilla gorilla gorilla) in Congo and Gabon. International Journal of Primatology, 33, 134-149


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

Captive breeding and reintroduction of primates into the wild: limited free-ranging experience Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla including captive bred individuals alongside 14 other interventions, survived for at least four years and some reproduced. Twenty-one (84%) of 25 gorillas released in Congo and 22 (85%) of 26 gorillas released in Gabon survived for at least four years. Nine females gave birth to 11 infants, of which nine survived. One individual of the Congo group was born in captivity and seven of the Gabon group came from captive-breeding facilities. Forty-three individuals were rehabilitated wild-born orphaned gorillas. Prior to release, gorillas underwent quarantine, health checks and received preventative vaccinations. Gorillas were released in groups and allowed to adapt to local environment and supplemented with food before release. Gorillas were released into habitat with no resident gorillas. Gorillas were treated for parasites and when sick. So-called ‘problem’-animals were removed and relocated. Dead gorillas were clinically examined. Both sites were proclaimed protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

Remove and relocate ‘problem’ animals Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, the Republic of Congo and Batéké Plateau National Park, Gabon (3) found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that became ’problem’ animals and were therefore recaptured and relocated along with 14 other interventions, survived for at least four years and some reproduced. Twenty-one of 25 gorillas (84%) released in the Congo and 22 of 26 gorillas (85%) released in Gabon survived for at least four years. Nine females gave birth to 11 infants, of which nine survived. In the Congo, five reintroduced ‘problem gorillas’ (solitary males) were recaptured after they moved outside of their home range to a more densely human populated area and were relocated back to avoid potential human-gorilla conflicts. Prior to release, gorillas underwent disease screening during quarantine and received preventative vaccinations. Gorillas were released in groups and prior to release were allowed to adapt to local environment and supplemented with food. Gorillas were released into habitat with no resident gorillas to re-establish populations and were treated for parasites and when sick. Dead gorillas were examined to determine their cause of death and to avoid disease transmission. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-born animals. Both release sites were proclaimed protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

(Summarised by JJ)

Preventative vaccination of habituated or wild primates Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests in Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that received preventative vaccinations prior to release alongside 14 other interventions, survived for at least four years. Twenty-one of 25 gorillas (84%) released in Congo and 22 of 26 gorillas (85%) released in Gabon survived at least four years. Nine females gave birth to 11 infants, of which nine survived. Gorillas underwent disease screening during quarantine, were released in groups, in habitat with no resident gorillas, allowed to adapt to the local environment and supplemented with food prior to release. Released gorillas were treated for parasites and when sick. So-called ‘problem-animals’ were removed and relocated and bodies of dead gorillas were examined to determine their cause of death. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-born. Both sites were declared protected areas before reintroduction commenced. 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 before-and-after site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla survived over four years when dead individuals were examined to determine their cause of death alongside 14 other interventions. Twenty-one of 25 gorillas (84%) released in Congo and 22 of 26 gorillas (85%) released in Gabon survived for at least four years. Nine females gave birth to 11 infants, of which nine survived. Four individuals died at each release site; three individuals died of natural causes, two died after fights with other gorillas and three disappeared and were pressumed dead. Gorillas underwent disease screening and vaccinations during quarantine. Gorillas were released in groups in habitats with no resident gorillas, allowed to adapt to local environment and supplemented with food prior to release. Released gorillas were treated for parasites and when sick. So-called ‘problem-animals’ were removed and relocated. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-born. Both sites were proclaimed protected areas before reintroduction procedures. The study does not distinguish between the effects of the different interventions mentioned above.

Remove/treat external/internal parasites to increase reproductive success/survival Primate Conservation

A before-and-after site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that were treated for parasites alongside 14 other interventions, survived for at least four years. Twenty-one of 25 gorillas (84%) released in Congo and 22 of 26 gorillas (85%) released in Gabon survived over four years. Nine females gave birth to 11 infants, of which nine survived. Three groups received a deworming or a treatment for a skin condition, one and three years after release. Gorillas underwent disease screening and vaccinations during quarantine. They were released in groups, allowed to adapt to local environment and supplemented with food before release. To re-establish populations, gorillas were released into habitat with no resident conspecifics. Released gorillas were treated when sick. So-called ‘problem-animals’ were removed and relocated and dead gorillas were clinically examined. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-born. Both sites became protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

Implement quarantine for primates before reintroduction/translocation Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that underwent quarantine prior to release alongside 14 other interventions, survived over four years. Twenty-one of 25 gorillas (84%) released in Congo and 22 of 26 gorillas (85%) released in Gabon survived at least four years. Nine females gave birth to 11 infants, of which nine survived. Before release, gorillas underwent disease screening and received preventative vaccinations. Gorillas were released in groups and allowed to adapt to local environment and supplemented with food prior to release. Gorillas were released into habitat with no resident gorillas to re-establish populations. Released gorillas were monitored frequently, treated for parasites, recaptured when sick, treated and released again. So-called ‘problem-animals’ were removed and relocated and dead gorillas were clinically examined. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-borns. Both sites became protected areas before reintroduction commenced. The study does not distinguish between the effects of the different interventions mentioned above.

Legally protect primate habitat Primate Conservation

A before-and-after site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that were released into regions that received protected status alongside other interventions, survived for at least four years. Twenty-one of 25 gorillas (84%) released in Congo and 22 of 26 gorillas (85%) released in Gabon survived for at least four years. Nine females gave birth to 11 infants, of which nine survived. Released gorillas underwent disease screening and vaccinations during quarantine. Gorillas were released in groups, allowed to adapt to the local environment and supplemented with food prior to release. Gorillas were released into habitat with no resident gorillas to re-establish populations. Released gorillas were treated for parasites and when sick. So-called ‘problem-animals’ were removed and relocated and bodies of dead gorillas were examined to determine their cause of death. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-borns. Both sites were proclaimed protected areas before reintroduction procedures commenced. The study does not distinguish between the effects of the different interventions mentioned above.

Reintroduce primates into habitat where the species is absent Primate Conservation

A before-and-after, site comparison study in 1996–2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of western lowland gorillas Gorilla gorilla gorilla that were reintroduced into habitat where the species was absent, along with 14 other interventions, survived for at least four years and some reproduced. Twenty-one of 25 gorillas (84%) released in Congo and 22 of 26 gorillas (85%) released in Gabon survived for at least four years. Eleven infants were born, of which nine survived. Gorilla populations had previously been extirpated at both release sites. Forty-three reintroduced individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were born in captivity. Before release, gorillas were screened for diseases during quarantine and vaccinated. Gorillas were released in groups, allowed to adapt to the local environment, and supplemented with food prior to release. Released gorillas were treated for parasites and when sick. Bodies of dead gorillas were examined to determine their cause of death. Both sites were designated protected areas. The study does not distinguish between the effects of the different interventions mentioned above.

Rehabilitate injured/orphaned primates Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that most of reintroduced western lowland gorillas Gorilla gorilla gorilla including orphaned individuals that were rehabilitated before release into the wild along with 14 other interventions, survived for at least four years and some reproduced. Twenty-one (84%) of 25 gorillas released in Congo and 22 (85%) of 26 gorillas released in Gabon survived for at least four years. Forty-three individuals were confiscated and rehabilitated orphan wild-born gorillas. Eight gorillas were ex-situ captive-born individuals. Prior to release, gorillas underwent quarantine, health checks and preventive vaccination. Gorillas were released in groups into habitat with no gorillas. Individuals were allowed to adapt to local environment, supplemented with food prior to release and treated for parasites and when sick. So-called ‘problem’-animals were relocated and dead gorillas were examined. Both sites were proclaimed protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

Provide supplementary food for a certain period of time only Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that most reintroduced western lowland gorillas Gorilla gorilla gorilla that were provided with food during the release phase along with 14 other interventions, survived for at least four years. Twenty-one (84%) of 25 gorillas released in Congo and 22 (85%) of 26 gorillas released in Gabon survived for at least four years. Nine females produced 11 infants, of which nine survived. In Gabon, gorillas received daily supplementary feeding for 23 months and then for another 16 months post-release. Congo groups received minimal supplementary food. During quarantine, gorillas underwent disease screening and vaccinations. Gorillas were released in groups into habitat with no resident gorillas and allowed to adapt to local environment prior to release. Released gorillas were treated for parasites and when sick. So-called ‘problem’-animals were removed and relocated and dead gorillas were examined. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-borns. Both sites became protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

Treat sick/injured animals Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that were treated when sick alongside 14 other interventions, survived for at least four years. Twenty-one of 25 gorillas (84%) released in the Congo and 22 of 26 gorillas (85%) released in Gabon survived for at least four years. Nine females gave birth to 11 infants, of which nine survived. Four individuals died at each release site. Two females were removed temporarily for treatment of critical injuries, and then re-released. Prior to release, gorillas underwent disease screening during quarantine and were vaccinated and treated for parasites. Gorillas were released in groups, allowed to adapt to local environment, and supplemented with food prior to release. Gorillas were released into habitat with no resident gorillas to re-establish populations. So-called ‘problem-animals’ were removed and relocated and dead gorillas were examined to determine their cause of death. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-borns. Both sites became protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

Allow primates to adapt to local habitat conditions for some time before introduction to the wild Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that were allowed to adapt to local environment before release along with 14 other interventions, survived at least four years. Twenty-one (84%) of 25 gorillas released in Congo and 22 (85%) of 26 gorillas released in Gabon survived over four years. Nine females gave birth to 11 infants, of which nine (82%) survived. In Gabon, gorillas were accompanied daily to the forest and spent the night in enclosures for an average of 15 months. In Congo, groups were either walked to the release site or brought there by vehicles and familiar staff. During quarantine, gorillas underwent disease screening and vaccinations. They were supplemented with food before release and released in groups into habitat with no resident wild gorillas. Released gorillas were treated for parasites and when sick. So-called ‘problem’-animals were removed and relocated and bodies of dead gorillas were examined. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-born individuals. Both sites became protected areas before reintroduction procedures. The study does not distinguish between the effects of the different interventions mentioned above.

Conduct veterinary screens of animals before reintroducing/translocating them Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of reintroduced western lowland gorillas Gorilla gorilla gorilla that underwent veterinary checks prior to release alongside 14 other interventions, survived over four years. Twenty-one of 25 gorillas (84%) released in the Congo and 22 of 26 gorillas (85%) released in Gabon survived for at least four years. Nine females gave birth to 11 infants, of which nine survived. Gorillas underwent disease screening and vaccinations during quarantine. Gorillas were released in groups and allowed to adapt to local environment and supplemented with food before release into habitat with no resident gorillas. Released gorillas were treated for parasites and when sick. So-called ‘problem-animals’ were removed and relocated and bodies of dead gorillas were examined to determine their cause of death. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight were ex-situ captive-born gorillas. Both sites became protected areas before reintroduction. The study does not distinguish between the effects of the different interventions mentioned above.

Reintroduce primates in groups Primate Conservation

A before-and-after, site comparison study in 1996-2006 in tropical forests of Lesio-Louna Wildlife Reserve, Republic of Congo (Congo) and Batéké Plateau National Park, Gabon found that the majority of western lowland gorillas Gorilla gorilla gorilla, reintroduced in groups along with 14 other interventions, survived for at least four years. Twenty-one (84%) of 25 gorillas released in Congo and 22 (85%) of 26 gorillas released in Gabon survived over four years. Nine females gave birth to 11 infants, of which nine survived. In Gabon, two groups were reintroduced in 2001 and 2004 and in Congo, five groups were reintroduced in 1996-2006. Gorillas underwent disease screening during quarantine and received preventative vaccinations. Gorillas were allowed to adapt to local environment and were supplemented with food prior to release. Gorillas were released into habitat with no resident gorillas. Released gorillas were treated for parasites and when sick. So-called ‘problem’-animals were removed and relocated and bodies of dead gorillas were examined. Forty-three individuals were rehabilitated wild-born orphaned gorillas and eight gorillas were ex-situ captive-borns. Both sites became protected areas before reintroduction commenced. The study does not distinguish between the effects of the different interventions mentioned above.