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Providing evidence to improve practice

Action: Rehabilitate injured/orphaned primates Primate Conservation

Key messages

  • One before-and-after study in Brazil found that most reintroduced golden lion tamarins did not survive over seven years, despite being rehabilitated, alongside other interventions. Two before-and-after studies in South Africa found that most reintroduced vervet monkeys survived over six months after being rehabilitated before release, alongside other interventions.
  • Two before-and-after studies in the Republic of Congo found that most reintroduced chimpanzees survived over 3.5–5 years after undergoing pre-release rehabilitation, alongside other interventions. One study in The Gambia found that numbers of reintroduced chimpanzees that underwent pre-release rehabilitation, alongside other interventions, increased by 38% over 25 years.
  • One review on bonobos, chimpanzees and gorillas in 13 African countries found that rehabilitated bonobos living in sanctuaries did not reproduce but the reproductive rate of chimpanzees was 14% and of gorillas was 2%.
  • One controlled study in Indonesia found that Bornean agile gibbons that were rehabilitated before release, alongside other interventions, behaved similarly to wild gibbons.
  • One controlled study in Malaysia found that numbers of reintroduced orangutans decreased by 33% over 33 years, despite orangutans being rehabilitated before release. One controlled study in Indonesia found that most translocated orangutans that were rehabilitated before release, along with other interventions, survived over three months.
  • One before-and-after, site comparison study in the Congo and Gabon found that most western lowland gorillas that were rehabilitated before release, alongside other interventions, survived over four years. One before-and-after study in Gabon found that one out of two western lowland gorillas that were reintroduced died despite being rehabilitated, alongside other interventions.

Supporting evidence from individual studies

1 

A before-and-after trial in 1984-1991 in coastal forest in Poço das Antas Reserve, Brazil found that over 60% of orphaned and rehabilitated golden lion tamarins Leontopithecus rosalia that were reintroduced into the wild alongside 14 other interventions, did not survive seven years. Fifty-eight (64%) out of 91 reintroduced tamarins did not survive over seven years. However, 57 infants were born (reproductive rate=63%), of which 38 (67%) survived. In contrast to the wild-born orphaned tamarins, captive-born tamarins never became independent of food and water provisioning and daily management. Different groups of captive-bred or orphaned tamarins were introduced in different years into habitat already occupied by the species and predators. Some groups were trained in behaviours that would facilitate survival, were provided with supplementary food, water and nesting boxes, and allowed to adapt to local conditions before release. Tamarins underwent quarantine, health checks and parasite treatment before release. Sick or injured animals were captured, treated and re-released. The reserve became officially protected in 1983. The study does not distinguish between the effects of the different interventions mentioned above.

2 

A before-and-after trial in 1996-1999 in tropical rainforest in Conkouati Reserve, Republic of Congo found that 14 out of 20 (70%) reintroduced wild-born orphaned chimpanzees Pan troglodytes troglodytes that were rehabilitated were still alive 3.5 years after release. Estimated mortality was 10-30%. None of the adult females reproduced. Chimpanzees fed on 137 different plant species, a variety similar to wild chimpanzees, and had activity budgets that resembled those of wild chimpanzees. No statistical tests were carried out to determine whether similarities were statistically valid. Orphan chimpanzees were rehabilitated and fostered at a sanctuary. Chimpanzees underwent veterinary screens, endoparasite treatments, and were vaccinated for poliomyelitis and tetanus. Before reintroduction in groups into habitat with low densities of resident wild chimpanzees, individuals spent 6-9 years on one of three forested islands in the region to acclimatize. Researchers were permanently on-site and monitored chimpanzees with radio-collars. The study does not distinguish between the effects of the different interventions mentioned above.

3 

A before-and-after trial in 1994-1999 in tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of rehabilitated orphaned chimpanzees Pan troglodytes troglodytes that were reintroduced along with 16 other interventions, survived for at least five years. Out of 20 reintroduced chimpanzees that were rehabilitated and socialized with other orphan chimpanzees in a sanctuary before release, 14 (70%) survived. No statistical tests were carried out to determine whether this decrease was significant. Individuals were radio-collared and followed at distances of 5-100 m. Chimpanzees underwent vaccination, parasite treatments and veterinary screens before being translocated in four subgroups to the release site with resident wild chimpanzees. Staff members were present to monitor health conditions, provide additional food when needed, and to examine dead animals. The area’s status was upgraded from reserve to national park in 1999. Local people were relocated from the release site to a nearby village. Some individuals were treated when sick or injured. TV and radio were used to raise awareness and local people were provided 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.

4 

A review in 1970-2001 on wild-born captive bonobos Pan paniscus, chimpanzees Pan troglodytes, and gorillas Gorilla spp. in 17 sanctuaries in 13 African countries found that bonobos did not produce offspring, but that overall reproductive rate of chimpanzees and gorillas in sanctuaries was 14% and 2%, respectively. In addition, 20% of great apes died prematurely. Only eight of the 17 sanctuaries in this study did not use birth control. Data were recorded with questionnaires distributed to sanctuary representatives via email. Only sanctuaries that were members of the Pan-African Sanctuary Alliance were included in the study. A total of 549 great apes were housed at the sanctuaries over the study period.

5 

A study in 1979-2004 in tropical forest on Baboon Islands, River Gambia National Park, The Gambia found that reintroduced western chimpanzees Pan troglodytes verus that were rehabilitated before releases along with other interventions, increased from 50 to 69 chimpanzees over 25 years. No statistical tests were carried out to determine whether this increase was significant. Fertility and mortality rates were similar to that of wild chimpanzees. However, infant mortality (18%) was lower than in wild populations. Other reproductive parameters were similar to those of wild chimpanzees. In total, 50 chimpanzees with various backgrounds and exposure to human care and handling were released on three islands. Nine of these had been received from traders, nursed back to health, and regularly taken into the forest for five years before being moved to Niokolo Koba National Park in Senegal, where they stayed for five years before being released to River Gambia National Park. Individuals were reintroduced in groups and into habitat with no chimpanzees but with predators (although these were rare) . They were provided with supplementary food daily or every second day. Individuals received periodic deworming, and were given antibiotic for severe colds. The study does not distinguish between the effects of the different interventions mentioned above.

6 

A controlled study in 2002-2003 in a swamp forest in Mintin Island, Borneo, Indonesia found that wild-born, captive-raised Bornean agile gibbons Hylobates albibarbis that were rehabilitated before release into the wild 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, the latter spent more time singing, socializing and travelling. Gibbons were quarantined for at least 12 months before reintroduction, during which they underwent veterinary screens. They were kept in in enclosures (3 x 3 x 3 m) and were supplemented with vitamins and leaves once a week. Individuals were introduced in pairs and into habitat in which wild gibbons were present. 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.

7 

A controlled study in 1967-2004 in tropical forest in Kabili-Sepilok Forest Reserve, Malaysia found that reintroduced orangutans Pongo pygmaeus morio that were rehabilitated before release into the wild along with eight other interventions, decreased by 33% over 33 years (1964-1997). Infant mortality (57%) was higher than in other wild and captive populations, and the sex ratio at birth was strongly biased towards females (proportion males: 0.11) compared to other wild and captive populations. However, inter-birth interval (6.1 years) was similar to wild populations of the same subspecies. Mean age at first reproduction (11.6 years) was lower than in other wild and captive populations. Orangutans were provided with daily supplementary food. Individuals underwent veterinary checks and 90 days of quarantine before being released into the reserve, where other rehabilitated orangutans lived. Injured or sick individuals were captured and treated. Staff and volunteers received medical checks and tourists had to keep safety distances (>5 m) at all times. The study does not distinguish between the effects of the different interventions mentioned above.

8 

A controlled study in 2004-2005 in secondary tropical forest in Bukit Tigapuluh National Park, Central Sumatra, Indonesia found that all reintroduced orphaned Sumatran orangutans Pongo abelii that were rehabilitated before reintroduction into the wild along with other interventions, survived for at least three months. All eight captive orphaned orangutans survived for at least three months after release. Orangutans underwent quarantine and health checks before being released to re-establish populations in habitat where previously-released orangutans occurred. Supplementary food was provided regularly. One group was released after a 6-month acclimatization phase at a sanctuary. Another group was kept in semi-free conditions for 7-9 months prior to release and could overnight in the enclosure. Staff members guided the latter to the forest on a daily basis. The study does not distinguish between the effects of the different interventions mentioned above.

9 

A before-and-after trial in 2009-2010 in coastal forest in Ntendeka Wilderness Area, Kwazulu-Natal, South Africa found that over half of reintroduced, captive, wild-born vervet monkeys Chlorocebus aethiops that were rehabilitated before release into the wild along with other interventions, survived for at least six months after release. Three individuals (19%) died. Two were killed by predators and one by domestic hunting dogs Canis lupus familiaris. Four individuals (25%) disappeared. One female gave birth to an infant two weeks after release. Individuals were rehabilitated in a 306.72 m2, 3.2 m high enclosure built on open grassland and enriched with pole-planted trees, hanging tyres, ropes, shade cloth hammocks, and a shaded shelter. Monkeys were introduced as one troop of 16 individuals into habitat without resident vervets and with predators. Monkeys spent one day in a release enclosure (49 m2). Supplementary food was provided twice per day for two weeks and daily during three weeks after release. The release site was protected as a wilderness area. The study does not distinguish between the effects of the different interventions mentioned above.

10 

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.

11 

A before-and-after trial in 2008 in a coastal forest at Isishlengeni Game Farm, Kwazulu-Natal, South Africa found that 62% of reintroduced vervet monkeys Chlorocebus aethiops that were rehabilitated before release into the wild along with other interventions, survived for at least six months. Five (17%) of 29 introduced individuals died. Of these, one died of predation and four were killed by domestic dogs Canis lupus familiaris. Six (21%) individuals disappeared. No females reproduced. Monkeys were rehabilitated in a 306.72 m2, 3.2 m high enclosure built on open grassland and enriched with pole planted trees, hanging tyres, ropes, shade cloth hammocks, and a shaded shelter. Monkeys were introduced as one troop of 29 individuals into habitat with wild vervets and predators. Individuals acclimatized by spending two nights in a release enclosure (49 m2) before being released. Monkeys were provided daily supplementary food. Medical care was provided when necessary before release and while housed. The study does not distinguish between the effects of the different interventions mentioned above.

12 

A before-and-after trial in 2008-2010 in a tropical forest-grassland mosaic at Batéké Plateau National Park, Gabon found that only one of two confiscated wild-born orphaned western lowland gorillas Gorilla gorilla gorilla that were rehabilitated before their reintroduction into the wild along with ten other interventions, survived for at least nine months. The group was reintroduced into habitat with predators and without resident gorillas. They were allowed to adapt to local conditions and spent the night in an enclosure equipped with nesting platforms, nesting material, supplementary food and water. Gorillas were dewormed regularly on-site. Caretakers guided them into different forest patches on a daily basis. 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.