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Providing evidence to improve practice

Action: Reintroduce primates into habitat where the species is present Primate Conservation

Key messages

  • Four before-and-after studies in Guinea and the Republic of Congo found that the majority of reintroduced chimpanzees survived for at least one to five years after reintroduction into habitat where the species was present, alongside other interventions. One study in Uganda found that a reintroduced chimpanzee repeatedly returned to human settlements after reintroduction intro habitat where the species was present, alongside other interventions, while a study in Senegal found that a reintroduced chimpanzee was reunited with its mother.
  • One study in Malaysia found that a majority of reintroduced orangutans survived reintroduction intro habitat where the species was present, alongside other interventions. One controlled study in Malaysia found that a reintroduced population of orangutans had declined 33 years after reintroduction into habitat where the species was present, alongside other interventions.
  • One study in Belize found that primate population increased five years after reintroduction into habitat where the species was present, alongside other interventions, while one study in Thailand found that primate population declined post-reintroduction.
  • Six studies in Brazil, French Guiana, Indonesia, Madagascar, and South Africa found that a minority of primates survived for at least fifteen weeks to seven years after reintroduction into habitat where the species was present, alongside other interventions. Five studies in Brazil, French Guiana, Gabon, and South Africa found that a majority of primates survived for at least two months to one year.
  • Two controlled studies in Madagascar and Indonesia found that reintroduced primates had similar diets to individuals in wild populations after reintroduction into habitat where the species was present, alongside other interventions. One controlled study in Indonesia found that reintroduced primates showed similar behaviour to wild individuals after reintroduction into habitat where the species was present, alongside other interventions. One study in Brazil found that a reintroduced muriqui rejoined a wild group after reintroduction into habitat where the species was present, alongside other interventions.

Supporting evidence from individual studies

1 

A before-and-after trial in 1984–1991 in coastal forest in Brazil found that the majority of golden lion tamarins Leontopithecus rosalia that were reintroduced into habitat alongside 14 other interventions, did not survive for more than seven years. Fifty-eight of 91 reintroduced tamarins (64%) did not survive in the wild. Fifty-seven infants were born (reproductive rate=63%) of which 38 (67%) survived. All groups had encounters and exchanged vocalizations with wild tamarins and one reintroduced male reproduced with a wild female. Different groups of captive-bred or orphaned tamarins were introduced in different years into habitat with predators. Before release some tamarins were trained to facilitate their wild survival, provided with supplementary food, water and nesting boxes, and allowed to adapt to local habitat conditions. Tamarins were quarantined, underwent veterinary checks, and were treated for parasites before their release. Reintroduced sick or injured animals were rescued, treated and re-released. The reserve was officially protected in 1983. The study does not distinguish between the effects of the different interventions mentioned above.

2 

A study, which was included in a review, in 1976–1977 in a protected forest in Thailand on captive lar gibbons Hylobates lar that were reintroduced, along with other interventions, found that their population decreased by 6% and that no infants were born in the 17 months after release. No statistical tests were carried out to determine whether this decrease was significant. One male was recaptured, removed and treated after being injured by wild gibbons. Four gibbons joined wild groups. A total of 31 gibbons were introduced. Anaesthetized gibbons were either kept in separate cages for 14 days before release, or laid on the forest floor. Injured animals were recaptured and treated. In 1961, gibbons were officially protected by national legislation. The study does not distinguish between the effects of the different interventions mentioned above.

3 

A before-and-after trial in 1994 in tropical forest in Brazil found that the majority of golden lion tamarins Leontopithecus rosalia that were translocated from degraded forest patches to protected habitat already occupied by the species, survived for at least two months. All seven monkeys (five adults and two infants) that were captured and translocated survived for at least two months after their release and increased their range over time. No statistical tests were carried out to determine whether this increase was significant. Tamarins were captured by baited traps, weighed, tattooed and all adults were fitted with radio-collars before release. The study does not distinguish between the effects of the different interventions mentioned above.

4 

A before-and-after trial in 1992–1997 in tropical forest in Belize found that the population wild black howler monkeys Alouatta pigra that was reintroduced, alongside other interventions, increased over time. No statistical tests were carried out to determine whether this increase was significant. Survival rate for monkeys reintroduced in 1992–1994 after between one month and 2 years was 86–100%. Birth rate was 20% (12 monkeys) and infant survival rate was 75% (9 of 12 monkeys). After 5 years, the population had increased from 62 to >100 individuals. Social groups were reintroduced, and 10 of the 14 groups were held in cages before release into habitat. Before release all individuals were screened by vets, were individually and permanently marked, and adults were fitted with telemetry collars. Hunting was largely controlled in the area and the local community was educated about conservation through multimedia campaigns. The study does not distinguish between the effects of the different interventions mentioned above.

5 

A study in 1993 in three tropical forest sites in Sabah, Malaysia found that along with other interventions, translocation of orangutans Pongo pygmaeus morio to an area where resident orangutans lived resulted in the survival of 78 of 80 (98%) individuals. Orangutans were either immobilized in trees or captured manually on the ground with nets. Nets were used to catch animals falling from trees during capture. Before release orangutans were screened by vets and sick animals were treated. Females were kept in separate cages from offspring and adequate space was maintained between occupied cages during temporary holdings and transportation. The study does not distinguish between the effects of the different interventions mentioned above.

6 

A study in 1994 in a tropical dry forest in Minas Gerais, Brazil found that an abandoned infant muriqui Brachyteles arachnoides that was removed from its natural habitat and then returned, along with other interventions, was retrieved by its mother and re-joined the wild group. Twenty-seven hours after detection of the infant, it was released near its mother who retrieved it immediately and re-joined the group again. The 4-month old female infant muriqui was removed from the forest ground and was given a blanket for warmth, fed with milk and supplementary food, and some ectoparasites were removed for study. The study does not distinguish between the effects of the different interventions mentioned above.

7 

A before-and-after-trial in 1995 in a montane forest in Uganda found that a captive female, wild-born chimpanzee Pan troglodytes schweinfurthii that was, along with other interventions, reintroduced into a human-habituated community of wild chimpanzees, repeatedly returned to human settlements after its release and was subsequently returned to captivity. Eight days after its initial release, the chimpanzee left the forest for the first time and was returned to the forest. For the following ten days, it travelled, fed, nested and engaged in social activities with the wild community. During this time, it increased ranging distance to humans and use of height, and visually monitored humans less regularly. The chimpanzee was returned to captivity six weeks after her release. It underwent pre-release training for three weeks before reintroduction. During this time, it was tested for tuberculosis and was quarantined. The study does not distinguish between the effects of the different interventions mentioned above.

8 

A study in 1994–1995 in a forest in French Guiana found that less than half of the red howler monkeys Alouatta seniculus that were translocated and reintroduced into habitat already occupied by the species alongside other interventions, survived over 18 months. Of 16 females monitored only seven (44%) survived for 18 months. Two monkeys died from screwworm fly larvae infestations under radio-collars and one from trauma. Three of the 16 females gave birth after release, but all infants disappeared and probably died shortly afterwards. All females studied for longer than three months (50%) settled within the release area. Of the 11 documented translocated troops 10 (91%) broke apart after release. Overlapping home ranges and/or social interactions between translocated and resident animals were observed. Before release all animals were screened by vets, were allowed to adapt to local conditions, and were reintroduced in groups. The study does not distinguish between the effects of the different interventions mentioned above.

9 

A before-and-after trial in 1996–1999 in a tropical rainforest in Conkouati Reserve, Republic of Congo found that reintroduction of wild-born orphaned chimpanzees Pan troglodytes troglodytes alongside eight other interventions resulted in 70% survival after three and a half years. Ten percent of reintroduced chimpanzees were confirmed to have died after three and a half years but this was possibly as high as 30%. No adult females produced offspring. Chimpanzees fed on 137 different plant species, a variety in diet similar to wild chimpanzees, and had activity budgets that resembled those of wild chimpanzees. However, no tests were carried out to determine whether differences were statistically significant or not. Adult females associated regularly with wild males during periods of oestrus. Before reintroduction in groups, 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. After this, chimpanzees were screened by vets, were treated for endoparasites, and vaccinated. The study does not distinguish between the effects of the different interventions mentioned above.

10 

A before-and-after trial in 1994–1999 in a tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of central chimpanzees Pan troglodytes troglodytes that, alongside 16 other interventions, were reintroduced into a habitat with resident wild chimpanzees survived for at least five years. Fourteen of the 20 (70%) reintroduced chimpanzees that had contact with resident wild chimpanzees, survived. No statistical tests were carried out to determine whether the population decrease was significant. Individuals were radio-collared and followed at distances of 5-100 m. Before being translocated rehabilitated orphaned chimpanzees were vaccinated, treated for parasites, and screened by vets. Staff members were present to monitor primate health, provide animals with additional food if necessary, and determine the cause of death of dead animals. The area was designated a national park in 1999. Local people were relocated from the release site to a nearby village. In some cases, local people were treated when sick or injured. TV and radio advertisements were used to raise awareness of chimpanzee conservation and local people were provided with monetary and non-monetary benefits in exchange for their conservation support. The study does not distinguish between the effects of the different interventions mentioned above.

11 

A before-and-after trial in 1994–1995 in tropical forest in French Guiana found that most of the translocated white-faced sakis Pithecia pithecia that were released into habitat with resident sakis along with other interventions, survived for at least four months. Two out of three translocated sakis survived for at least four months after release and one individual died after approximately 22 weeks. The female bonded with one of the two released males. Three out of six translocated sakis were monitored for 41 weeks after release. Sakis were captured using nets, tagged with radio transmitters and were screened by vets before release. When dead sakis were detected, the cause of death was determined. The study does not distinguish between the effects of the different interventions mentioned above.

12 

A before-and-after trial in 1998–1999 in tropical forest on an island in French Guiana found that a small number of squirrel monkeys Saimiri scireus that were reintroduced into a habitat already occupied by resident monkeys along with other interventions, survived for 15 weeks after reintroduction. Six of 14 released monkeys (43%) survived for 15 weeks. Two individuals died in release cages, and one was assumed to have been killed by resident squirrel monkeys. One month after release, five monkeys were rescued and brought back to captivity. All six remaining monkeys were wild-born. Eleven weeks after reintroduction, two resident monkeys entered the release group. Animals were kept as one group in a cage at the captive colony where two females gave birth. After transfer to the release site, they were held in an enclosure to adapt to local habitat conditions. The study does not distinguish between the effects of the different interventions mentioned above.

13 

A controlled study in 1998–2001 in tropical forest in Madagascar found that captive-bred black-and-white ruffed lemurs Varecia variegata variegata that were reintroduced into habitat already occupied by the species, along with other interventions, did not have a similar diet to that of the resident wild group one year after release. Captive-bred lemurs (one male and two females) fed only on slightly more than half of the plant species (57 plant species) that the wild group (ten individuals) fed on (109 plant species). Captive-bred lemurs did not closely follow the dietary choices and seasonal changes in diet exhibited by the wild group, although no statistical tests were carried out to determine whether this difference was significant. Lemurs were released in groups and were provided with supplementary food. The study does not distinguish between the effects of the different interventions mentioned above.

14 

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.

15 

A controlled study in 1997–2001 in tropical forest in Betampona Reserve, Madagascar found that diets of captive-bred black-and-white ruffed lemurs Varecia variegata variegata that were born and raised in a free-ranging environment and were later reintroduced into habitat already occupied by the species along with other interventions, overlapped with that of the resident wild group. No statistical tests were carried out. Reintroduced lemurs (three males and two females) fed on 92 species over three years, while the wild group (ten individuals) fed on 109 species over four years. Reintroduced lemurs consumed less foliage throughout the study and less nectar in 1998 than the wild group did, although no statistical tests were carried out to determine whether this difference was significant. Two males died of malnutrition in 1998. Lemurs were introduced in groups and provided supplementary food during resource-scarce periods. The study does not distinguish between the effects of the different interventions mentioned above.

16 

A controlled study in 2002–2003 in lowland freshwater swamp forest in Borneo, Indonesia found that wild-born, captive-raised Bornean agile gibbons Hylobates albibarbis reintroduced into habitat in which wild gibbons were present along with other interventions, shared a similar diet, spent similar amounts of time feeding, resting, and arm-swinging and at similar canopy heights as wild gibbons. However, wild gibbons spent more time singing, socializing, and travelling. Before reintroduction, gibbons were quarantined in enclosures (3 x 3 x 3 m) for at least 12 months, were screened by vets were allowed to socialize and acclimatize to the natural environment, and were supplemented with vitamins and leaves once a week. Only one reintroduced pair of gibbons was compared to a pair of wild gibbons at another site. The study does not distinguish between the effects of the different interventions mentioned above.

17 

A controlled study in 1967–2004 in tropical forest in Kabili-Sepilok Forest Reserve, Malaysia found that reintroduction, along with eight other interventions, resulted in a 33% decline in the population of reintroduced, rehabilitated orangutans Pongo pygmaeus morio after 33 years. Infant mortality (57%) was higher than in other wild and captive populations, and sex ratio at birth was strongly biased towards females (proportion of males=0.11) as compared to other wild and captive populations. However, the time between births (6.1 years) was shorter than in other orangutan subspecies or species in the wild and in captivity, but similar to wild populations of the same subspecies. Average age at first reproduction (11.6 years) was lower than in other wild and captive populations. Orangutans were continuously provided with supplementary food from 2-7 feeding platforms. Before release individuals underwent in-depth veterinary checks and were kept under quarantine for 90 days. Individuals were captured and treated when they displayed signs of injury or illness. Tourists were informed to keep >5 m from animals at all times. The study does not distinguish between the effects of the different interventions mentioned above.

18 

A study in 2002–2006 in tropical forest in Gabon found that approximately one third of captive-bred mandrills Mandrillus sphinx that were reintroduced into habitat occupied by wild mandrills, along with other interventions, had died one year after release. Mortality was 33% (12/36), with dependent infants being most affected. Fertility rate was 42% (5/12 females), and two of the five infants survived for longer than six months. Mortality decreased to 4% in the second year and fertility rate remained at 42% and all five infants born survived for at least six months. Their range remained limited during the first two years after release. In 2004, a solitary wild male took over the group, after which the group extended its range. Mandrills were reintroduced as a group into habitat with predators, allowed to adapt to local habitat conditions for some time, and treated for endoparasites before release. Supplementary feeding was provided until 2005. The study does not distinguish between the effects of the different interventions mentioned above.

19 

A study in 2009 in savanna in Senegal found that reintroducing into the wild of a confiscated 9-month old female infant chimpanzee Pan troglodytes verus resulted in succesul reunion with its mother in habitat where other resident wild chimpanzees occurred. Reintroduction was carried alongside other interventions. Four days after confiscation, the chimpanzee was released in the vicinity of its natal group, which retrieved it immediately. The infant’s natal group was located and the infant was released close to the group. The infant was also treated for its injured eye. During handling of the infant surgical masks were worn and hands were sanitized when handling the infant and its food. The study does not distinguish between the effects of the different interventions mentioned above.

20 

A before-and-after trial in 2007–2008 in a dry forest in KwaZulu-Natal, South Africa found that vervet monkeys Chlorocebus aethiops that were reintroduced into habitat with resident vervets along with other interventions, survived for at least 10 months after reintroduction. Out of 35 monkeys released, six (17%) survived, 22 (63%) vervets went missing, and seven (20%) died. Two infants were born after release. Out of 24 vervets released in a second reintroduction, 12 (50%) survived, seven (29%) went missing, and five (21%) died. Both troops had aggressive interactions with resident vervets and wild males were seen near reintroduced monkeys several times. Before release, monkeys were checked by vets, and allowed to adapt to local environmental conditions. Monkeys received supplementary food and water after release. The study does not distinguish between the effects of the different interventions mentioned above.

21 

A before-and-after trial in 2008–2010 in dry forest in Guinea found that the majority of wild-born orphaned western chimpanzees Pan troglodytes verus that were reintroduced into habitat with wild chimpanzees along with other interventions, survived reintroduction and remained free-living for at least 27 months. One (8.3%) of the 12 released chimpanzees died. One female returned to the sanctuary voluntarily and one male was returned after suffering injuries during a recovery mission. Five chimpanzees (42%) remained together at the release site. Two infants were born, both of which survived. Another female immigrated and integrated into a wild chimpanzee community and three chimpanzees moved to an area away from the release site. One male was observed to have suffered injuries to his genitals and face that were presumably inflicted by resident wild chimpanzees. All reintroduced chimpanzees were screened for diseases before their release into habitat with predators. Some chimpanzees were allowed to acclimatize to local habitat conditions prior to release. Chimpanzees were initially supplemented with food on a daily-, and later on, a weekly basis. The study does not distinguish between the effects of the different interventions mentioned above.

22 

A before-and-after trial in 2008 in a coastal forest in Kwazulu-Natal, South Africa found that 62% of rehabilitated vervet monkeys Chlorocebus aethiops that were reintroduced into habitat already occupied by wild vervets along with other interventions, survived for at least six months. Five of 29 introduced individuals (17%) were reported dead. Of these, one died of predation and four were killed by domestic hunting dogs Canis lupus familiaris. Six individuals (21%) went missing. No females reproduced. Medical care was provided when necessary before release and while housed at the nearby rehabilitation centre. Before being released monkeys spent two nights in a release enclosure (49 m2). Monkeys were provided daily supplementary food. The study does not distinguish between the effects of the different interventions mentioned above.

23 

A before-and-after trial in 2006–2011 in tropical forest in Indonesia found that very few reintroduced Javan slow lorises Nycticebus javanicus and greater slow lorises N. coucang that were released into habitat with resident lorises along with other interventions, survived for at least 146 and 22-382 days, respectively. Out of five reintroduced greater slow lorises, one survived for at least 146 days and out of 18 reintroduced Javan slow lorises, five individuals (28%) survived for at least 22–382 days. No interaction with wild lorises was reported. Before being released individually lorises were quarantined and screened by vets. Sick individuals were recaptured and treated. Twenty-one lorises were held in enclosures at the release site to adapt to local habitat where predators occurred. Bodies of dead lorises were examined to determine their cause of death. The study does not distinguish between the effects of the different interventions mentioned above.

Referenced papers

Please cite as:

Junker, J., Kühl, H.S., Orth, L., Smith, R.K., Petrovan, S.O. & Sutherland, W.J. (2018) Primate conservation. Pages 393-445 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.