Providing evidence to improve practice

Individual study: Successful reproduction of wild-released orphan chimpanzees Pan troglodytes in Conkouati-Douli National Park, Republic of Congo

Published source details

Goossens B., Setchell J.M., Vidal C., Dilambaka E. & Jamart A. (2003) Successful reproduction in wild-released orphan chimpanzees (Pan troglodytes troglodytes). Primates, 44, 67-69


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

Reintroduce primates into habitat with predators Primate Conservation

A before-and-after trial in 1996–2001 in a tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of 36 wild-born orphan chimpanzees Pan troglodytes troglodytes that were reintroduced into habitat with predators along with other interventions, survived for at least 1-5 years. Twenty-six of 36 chimpanzees survived and only three were confirmed dead, of which none were reported to have been killed by predators. The remaining seven chimpanzees disappeared, resulting in a minimum survival rate of 72%, with a possible 92%. One infant, whose parents were both released in 1996, was born in 2001. Chimpanzees were rehabilitated on islands before their introduction into habitat already occupied by wild chimpanzees. After release, individuals were equipped with radio transmitters and followed regularly by local staff to record data on cycling status, interactions with resident wild chimpanzees, and sexual behaviour. Parentage was determined by analysing DNA extracted from hairs of all released chimpanzees and infants. Injured chimpanzees received veterinary care. The study does not distinguish between the effects of the different interventions mentioned above.

Treat sick/injured animals Primate Conservation

A before-and-after study in 1996-2001 in tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of wild-born orphan chimpanzees Pan troglodytes troglodytes reintroduced into the wild and treated when injured or sick along with other interventions, survived for at least 1-5 years. Twenty-six of 36 released chimpanzees survived until the end of the study in 2001 and only three chimpanzees were confirmed dead; none were killed by predators. The remaining seven chimpanzees disappeared, giving a survival rate of 72-92%. One infant, whose parents were both released in 1996, was born in 2001. One released male was seriously injured by a wild male and another released male in 1997 and 1999 and underwent veterinary interventions on both occasions. Released individuals were radio-collared and followed. Chimpanzees were rehabilitated on islands before their introduction into habitat with both wild chimpanzees and predators. 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 trial in 1996-1999 in tropical rainforest in Conkouati Reserve, Republic of Congo found that 70% of reintroduced wild-born orphaned central chimpanzees Pan troglodytes troglodytes that underwent veterinary screens along with eight other interventions, were still alive 3.5 years post-release. Confirmed mortality was 10%, with a possible 30%. None of the adult females produced offspring. Chimpanzees fed on 137 different plant species, diversity in diet similar to that of wild chimpanzees, and had activity budgets that resembled those of wild chimpanzees. No statistical tests were carried out to determine whether similarities were significant. Chimpanzees were treated for internal parasites and vaccinated for poliomyelitis and tetanus. Before reintroduction in groups into habitat with low densities of wild chimpanzees, they spent 6-9 years on one of three forested islands in the region to acclimatize. Orphan chimpanzees were rehabilitated and fostered at a nearby sanctuary. Researchers were permanently present on-site and monitored released chimpanzees using radio-collars. 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 trial in 1996-2001 in tropical lowland forest in Conkouati-Douli National Park, Republic of Congo found that the majority of wild-born orphan chimpanzees Pan troglodytes troglodytes that were allowed to adapt to local habitat conditions for some time before reintroduction, along with other interventions, survived for over five years. Twenty-six of 36 released animals survived over five years and only three died. Seven chimpanzees disappeared, resulting in an estimated survival of 72-92%. An infant was born after five years.. Chimpanzees were rehabilitated on islands where they were provided with food before their reintroduction to the mainland. After release, individuals were radio-collared and followed to record female cycling status, interactions with wild chimpanzees and sexual behaviour. Analysis of hair-extracted DNA of all released chimpanzees and infants was used to determine parentage. Chimpanzees were released into a forest where wild chimpanzees and predators were known to exist. Injured chimpanzees were treated. The study does not distinguish between the effects of the different interventions mentioned above.

Reintroduce primates into habitat where the species is present Primate Conservation

A controlled study in 2001 in tropical forest in Madagascar found that captive-bred black-and-white ruffed lemurs Varecia variegata variegata that had limited free-ranging experience before they were reintroduced into habitat already occupied by the species, along with other interventions, had similar diets to that of the resident wild group. Reintroduced lemurs (three males and one female) fed on 54 species during a single year, as compared to the wild group (ten individuals) that fed on 109 species over four years. Reintroduced lemurs consumed less foliage than the wild group, although no statistical tests were carried out to determine whether this difference was significant. Lemurs were introduced in groups into habitat already occupied by the species and provided supplementary food during resource-scarce periods. The study does not distinguish between the effects of the different interventions mentioned above.