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Providing evidence to improve practice

Action: Treat sick/injured animals Primate Conservation

Key messages

  • Two before-and-after studies in Brazil found that most reintroduced golden lion tamarins died despite being treated when sick or injured, alongside other interventions. One study in Brazil found that one out of four reintroduced black lion tamarins died after being release despite receiving treatment, alongside other interventions.
  • One review on reintroduced lar gibbons in Thailand found that their population declined by 6% seventeen months after release despite having medical treatment available when sick or injured, alongside other interventions.
  • One study in Malaysia found that 98% of translocated orangutans, some of which received treatment for injuries along with other interventions, survived capture and subsequent release. One controlled study, also in Malaysia, found that a population of reintroduced orangutans decreased by 33% over 33 years despite receiving treatment when sick or injured, alongside other interventions.
  • Four studies, including two before-and-after studies, in Liberia, the Republic of Congo and The Gambia found that most reintroduced chimpanzees that were treated when sick, alongside other interventions, survived for at least 1-5 years and in one case the population increased. One study in Senegal found that a young chimpanzee was reunited with its mother after being treated for injuries, alongside other interventions.
  • One before-and-after study in Uganda found that treatment for mange, alongside other interventions, cured some infected mountain gorillas. One study in Rwanda, Uganda and the Democratic Republic of Congo and one before-and-after, site comparison study in the Republic of Congo and Gabon found that most western lowland gorillas treated when sick or injured, alongside other interventions, survived over 4–41 years.
  • Two before-and-after studies in South Africa and Indonesia found that most reintroduced or translocated primates that were treated when sick, alongside other interventions, survived over six months. However, two before-and-after studies in Madagascar and Kenya found that most reintroduced or translocated primates did not survived over five years or their population size decreased despite treated when sick, alongside other interventions.

Supporting evidence from individual studies

1 

A before-and-after trial in 1954-1985 in a degraded rainforest in Poço das Antas Reserve, Brazil found that a translocated population of captive-born golden lion tamarin Leontopithecus rosalia of which sick or injured individuals were removed from the wild and medically treated along with nine other interventions, decreased by 57% within the first year post-release. No statistical tests were carried out to determine whether this difference was significant. Of the 14 individuals released, seven died and two were removed and treated. Three infants were born, one of which died from illness. Eight individuals were released as a family group and six individuals were released as pairs one month later. Tamarins spent an unknown amount of time in 15 x 4.5 x 3 m outside enclosures to acclimatize. They were habituated to humans and fostered to facilitate survival in the wild. The reserve included natural predators. Reintroduced tamarins were supplied with food for 10 months post-release. Artificial nesting boxes were also put up in the reserve. The study does not distinguish between the effects of the different interventions mentioned above.

2 

A before-and-after trial in 1984-1991 in coastal forest in Poço das Antas Reserve, Brazil  found that the majority of reintroduced golden lion tamarins Leontopithecus rosalia, which were treated if sick or injured alongside 14 other interventions, did not survive over the study period of seven years. Fifty-eight out of 91 (64%) reintroduced tamarins did not survive in the wild. However, 57 infants were born (reproductive rate=63%) during the study, of which 38 (67%) survived. Reintroduced sick or injured animals were rescued, treated and only re-released once fully recovered. Tamarins were also screened and treated for parasites, infectious diseases, possible genetically-based defects. Different groups of captive-bred or orphaned tamarins were introduced in different years into habitat already occupied by the species and predators. Groups were quarantined, provided with supplementary food, water and nesting boxes, and allowed to adapt to local habitat conditions before release. The reserve became officially protected in 1983. The study does not distinguish between the effects of the different interventions mentioned above.

3 

A study, part of a review, in 1976-1977 in Sai Yok National Park, Thailand found that numbers of captive lar gibbons Hylobates lar that were released and treated when injured or sick alongside other interventions decreased by 6% and no infants were born 17 months post-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 as individuals, pairs, or family groups into habitat with resident wild gibbons. Anaesthetized gibbons were either kept in separate cages from which they could hear, but not see each other for 14 days before release, or laid out on the forest floor. In 1961, gibbons became officially protected in Thailand. Permanent presence of area managers and other staff appeared to ensure protection from hunters. The study does not distinguish between the effects of the different interventions mentioned above.

4 

A study in 1993 in fragmented tropical forest in Sabah State, Malaysia found that 78 of 80 (98%) translocated orangutans Pongo pygmaeus morio, some of which were treated for injuries alongside other interventions, survived capture and subsequent release at Tabin Wildlife Reserve. Four individuals escaped from their temporary holdings before they could be transported to the release site. Of these, three individuals suffered minor injuries and one individual sustained major injury during capture, but all were treated successfully. Orangutans were either immobilized in trees or captured manually on the ground with nets. Individuals underwent veterinary screens before they were released individually into habitat already occupied by other orangutans. To avoid injury due to post-traumatic stress, females were kept in separate (but adjacent) cages from their 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.

5 

A study in 1987-1988 on an island with tropical forest in Liberia, West Africa found that the majority of reintroduced western chimpanzees Pan troglodytes verus that were treated when sick alongside other interventions, survived for at least one year post-release. Seven out of 30 released chimpanzees had difficulties to adjust and were brought back into captivity. Three individuals were temporarily removed after release for medical treatment of injuries due to fights with other chimpanzees. Chimpanzees were screened for diseases before they were released in groups. Furthermore, they were socialized in naturalistic enclosures and were taught behaviour to facilitate their survival in the wild. On site, primates were allowed to adapt to the local habitat in enclosures for some time; younger and low-ranking individuals were released earlier to reduce stress. Released chimpanzees were continuously provided with food. The study does not distinguish between the effects of the different interventions mentioned above.

6 

A study in 1999 in tropical forest in Morro do Diabo State Park, São Paulo, Brazil found that only some of the individuals in a group of reintroduced wild and captive-bred black lion tamarins Leontopithecus chrysopygus had survived over four months post-release, although sick animals were treated alongside other interventions. Four months post-release of three individuals, one tamarin died. After being found weak and dehydrated nine days after his release, this male was recaptured, treated and released again 13 days later but was found dead some weeks later. Tamarins underwent veterinary screens before translocation to an enclosure at the release site where they could adapt to the local environment where predators occurred. The released group consisted of two wild females and one captive-born male raised in a free-ranging environment where he had been fostered natural behaviour to facilitate reintroduction. Monkeys were fitted with radio-transmitters and supplemented with food throughout the study. The study does not distinguish between the effects of the different interventions mentioned above.

7 

A before-and-after trial in 2000-2001 in tropical forest in Bwindi Impenetrable National Park, Uganda found that medically treating mountain gorillas Gorilla beringei beringei infected with mange, cured the animals. In a group consisting of 18 gorillas, some individuals were treated on site after detection of mild signs of mange. The number of treated gorillas was not included. Two doses of Ivermectin were administered by darting individual gorillas. In addition, when a skin infection was initially detected, skin scrapings were collected and biopsies conducted to confirm the preliminary diagnosis. Another five groups whose home ranges overlapped with that of the group that included individuals treated for mange, also showed signs of this disease. However, the authors mention that the infection was brought under control and that no deaths occurred.

8 

A before-and-after study in 1994-1999 in mixed tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of reintroduced chimpanzees Pan troglodytes troglodytes that were treated when injured alongside 16 other interventions, survived over five years. Out of 20 reintroduced chimpanzees that were occasionally treated for injuries caused by fights with other chimpanzees, 14 survived (70%). No statistical tests were carried out to determine whether the change was significant or not. Individuals were radio-collared and followed at distances of 5-100 m. Rehabilitated orphaned chimpanzees underwent vaccination, parasite treatment and veterinary screens before translocation in four subgroups from the sanctuary to the release site where resident chimpanzees already occurred. Staff members were permanently present to monitor their health, provide additional food if necessary and detect and examine dead animals. The area status was upgraded from reserve to national park in 1999. Local people were relocated from the release site to a nearby village. TV and radio advertisements were used to raise chimpanzee conservation 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.

9 

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.

10 

A before-and-after study in 1997-2002 in primary forest in Betampona Reserve, Madagascar found that less than half of all captive-bred, parent-reared, reintroduced black-and-white ruffed lemurs Varecia variegata variegata, which were recaptured and treated when sick alongside ten other interventions, survived over five years. Five of 13 individuals (38.5%) survived in the wild and six individuals were born, of which four survived. One female and one male of the group reproduced with wild resident lemurs and the male became fully integrated. Recaptures of sick animals for treatment were achieved using hand-grabbing. Released animals were monitored with radio-collars. Captive lemurs had limited semi-free-ranging experience, were quarantined and underwent veterinary screens before their reintroduction in groups into habitat with predators and wild lemurs. They were provided with supplementary food and water for a certain period of time and allowed to adapt to local habitat conditions before release. Dead lemurs were detected and their cause of death investigated. The study does not distinguish between the effects of the different interventions mentioned above.

11 

A controlled, before-and-after trial in 1973-2001 in savannah at the Chololo ranch, Laikipia Plateau, Kenya found that a population of translocated crop-raiding olive baboons Papio anubis survived over 17 years when some individuals received medical treatments when sick alongside with other interventions. A total of 94 baboons in two troups were translocated in 1984 and 62 individuals remained in 2001 (66% survival). One wild troop at the capture site and another resident troop at the release site served as control groups. Survival rates did not differ between control and study groups. Four females were treated for a bacterial infection but there were no other intervenitons since 1986. Both translocated troops were regarded as ‘problem animals’ by farmers and were released into habitat with resident wild baboons and predators. Before translocation, individuals underwent veterinary screens. In addition, a long-term research project was launched to study these animals. Post-release, baboons were briefly provided with food during periods of drought. The study does not distinguish between the effects of the different interventions mentioned above.

12 

A study in 1979-2004 in tropical forest on Baboon Islands, River Gambia National Park, The Gambia found that rehabilitated and reintroduced western chimpanzees Pan troglodytes verus that were treated when sick alongside other interventions, increased from 50 to 69 chimpanzees over 25 years. No statistical tests were carried out to determine whether this population increase was significant. Fertility and mortality rates were similar to that in wild chimpanzees, except for infant mortality (18%), which was lower than in wild populations. Inter-birth interval, average age at first birth, proportion males at birth, age at first sexual swelling in females, and adolescent infertility were all similar to that of wild chimpanzees. Individuals received periodic deworming and antibiotic treatment for severe colds. Chimpanzees were reintroduced in groups and into habitat with natural predators (although these were rare), but with no other chimpanzees. They were provided supplementary food every 1-2 days. The study does not distinguish between the effects of the different interventions mentioned above.

13 

A controlled study in 1967-2004 in tropical forest in Kabili-Sepilok Forest Reserve, Malaysia found that rehabilitated and reintroduced orangutans Pongo pygmaeus morio, which were captured and treated for injury or illness alongside 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). However, inter-birth-interval (6.1 years) was similar to wild populations of the same subspecies. Orangutans were provided with daily supplementary food from 2-7 feeding platforms. Mean age at first reproduction (11.6 years) was lower than in other wild and captive populations. Individuals underwent in-depth veterinary checks and were kept in quarantine for 90 days before they were released into the reserve, in which other rehabilitated orangutans lived. 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.

14 

A study in 2009 in savanna-woodland mosaic in Niokolo-Koba National Park, Senegal found that a confiscated female infant chimpanzee Pan troglodytes verus that was treated for injuries along with other interventions, was reunited with its mother in the wild. Four days after confiscation, the chimpanzee was released in the vicinity of its natal group, which retrieved it immediately. The estimated 9-months old female infant chimpanzee was treated for its injured eye which was almost completely healed before release. The infant’s natal group was located with the aid of poachers, after which the infant was released close to the group. The researcher wore a surgical mask and sanitized her hands when handling the infant and its food to prevent disease transmission. The study does not distinguish between the effects of the different interventions mentioned above.

15 

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.

16 

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.

17 

A before-and-after trial in January-July 2008 in a coastal forest at Isishlengeni Game Farm, Kwazulu-Natal, South Africa found that 62% of rehabilitated vervet monkeys Chlorocebus aethiops that were reintroduced into the wild and treated if they showed symptoms of disease before their release 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 on an ‘as required’ basis before release and while housed at the nearby rehabilitation centre. Monkeys were introduced as one troop of 29 individuals into habitat already occupied by wild vervets and with predators. To acclimatize, monkeys spent two nights in a release enclosure (49 m2) before being released. Monkeys were provided daily supplementary food. The study does not distinguish between the effects of the different interventions mentioned above.

18 

A before-and-after study in 2006-2011 in tropical forest at Gunung Halimun Salak National Park and Batutegi Nature Reserve, Indonesia found that only few reintroduced greater slow lorises Nycticebus coucang and Javan slow lorises N. javanicus that were treated when sick alongside other interventions, survived for at least 146 and 22-382 days, respectively. Out of five reintroduced greater slow lorises, only 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. Exact survival time was not provided. One Javan slow loris was recaptured and remained at a sanctuary after its arm was amputated. All lorises underwent quarantine and veterinary screens prior to single releases. All but two lorises were held in enclosures at the release site to adapt to local habitat conditions where conspecifics and 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.