Action

Reintroduce primates into habitat where the species is absent

How is the evidence assessed?
  • Effectiveness
    60%
  • Certainty
    40%
  • Harms
    0%

Source countries

Key messages

  • One study in The Gambia found that a population of reintroduced chimpanzees increased over 25 years after reintroduction into habitat where the species was absent, alongside other interventions.
  • One controlled study in Indonesia found that all Sumatran orangutans survived for at least three months after reintroduction into habitat where the species was absent, alongside other interventions.
  • One before-and-after study in the Republic of Congo found that a majority of reintroduced gorillas survived for at least four years after reintroduction into habitat where the species was absent, alongside other interventions.
  • One study in Thailand found that a reintroduced population of lar gibbons declined over three years following reintroduction into habitat where the species was absent, alongside other interventions. One study in India found that a population of reintroduced rhesus monkeys persisted for at least four years after reintroduction.
  • Six studies (including four before-and-after studies) in Belize, Gabon, Madagascar, Malaysia, South Africa, and Vietnam found that a majority of primates survived for two to thirty months after reintroduction into habitat where the species was absent, alongside other interventions. Two studies in Malaysia and Vietnam found that a minority of primates survived after between three months and 12 years.

About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A study, which was included in a review, in 1967–1970 on the island of Koh Klet Kaeo, Thailand found that reintroduction, along with other interventions, led to declines of 60% in the population of formerly captive lar gibbons Hylobates lar over three years. No statistical tests were carried out to determine whether this decrease was significant. Four infants were born to the introduced population of 20 gibbons (reproductive rate =20%). Twenty gibbons were introduced in pairs into habitat that did not resemble their natural habitat and without resident gibbons. Gibbons were obtained from commercial animal dealers and housed in a laboratory for at least one month along with the gibbon with whom they were released on the island. Gibbons were fed and provided with water from artificial food and water stations. In 1961, gibbons were officially protected by the Thai government. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  2. A before-and-after trial in 1976–1988 in a degraded tropical forest in Sarawak, Malaysia found that at least 77 of 87 (89%) captive, wild-born Müller's Bornean gibbons Hylobates muelleri that were reintroduced into habitat without resident wild gibbons along with other interventions, died after release. Confiscated gibbons had undergone veterinary checks and were placed in holding cages in a forest clearing. When possible, males and females were paired in cages prior to release. Müller's Bornean gibbons were protected under state law. Surveys of direct sightings and gibbon calls were conducted simultaneously by three or four observers on non-rainy days on eight mornings from 4 February to 31 March 1988. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  3. A replicated study in 1992–1993 in tropical forest in Belize found that the majority of reintroduced black howler monkeys Alouatta pigra that were released into habitat where no resident monkeys occurred, alongside other interventions, survived for at least ten months and reproduced. Twelve of 14 reintroduced monkeys (86%) survived for at least ten months after release. One monkey disappeared two months after release. Four infants were born in the release groups. Wild howlers had been captured at a sanctuary and were translocated to the site. Prior to release, monkeys were screened by vets. Monkeys were allowed to adapt to local habitat conditions before release. Six individuals were fitted with ball-chain radio collars and another six were implanted with radio-transmitters. Radio collars worked for 6-10 months, but transmitter signals were lost six weeks post-release. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  4. A replicated, before-and-after-trial in 1995–2001 in orchards in Mathura District, India found that rhesus monkeys Macaca mulatta reintroduced into forest patches without resident macaques along with other interventions, remained at their release sites for at least four years. A post-translocation study in 2001 confirmed that all of the 600 monkeys captured from 12 troops and translocated to eight different forest patches, had settled, were healthy, showed no signs of stress, and behaved normally. In addition, time spent engaging in different activities during the first three months after release was similar to activity budgets of wild groups in northern India. Monkeys were only moved to habitat without resident macaques, because no health checks were conducted on the captured monkeys and to avoid competition with resident troops. Captured monkeys were translocated to natural habitat, where they were reintroduced in groups. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  5. A study in 1979–2004 in tropical forest in The Gambia, found that the population of rehabilitated western chimpanzees Pan troglodytes verus that were reintroduced into habitat with no wild or previously reintroduced chimpanzees, along with other interventions, increased from 50 to 69 over 25 years. No statistical tests were carried out to determine whether this increase was significant. Fertility and mortality rates were similar to wild chimpanzees, except for infant mortality (18%), which was lower than in wild populations. Time between births, average age at first birth, proportion of males at birth, age at first sexual swelling in females, and adolescent infertility were similar to that of wild chimpanzees. In total, 50 chimpanzees from various backgrounds were released on three islands. Individuals were reintroduced in groups and into habitat with small populations of natural predators. They were provided supplementary food daily or on every second day, depending on which one of the islands they lived on. Individuals were periodically dewormed, and given antibiotic treatment when they suffered from severe colds. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  6. A before-and-after trial in 2006–2007 in rainforest in in Madagascar found that black-and-white ruffed lemurs Varecia variegata variegata and diademed sifakas Propithecus diadema that were translocated from disturbed sites to undisturbed habitat where the species was locally extinct, along with other interventions, survived for at least 30 months and reproduced. No deaths were recorded for black-and-white ruffed lemurs over a 30-months while one diademed sifaka died from natural causes. Four black-and-white ruffed lemur offspring twins (reproductive rate=57%) and seven diademed sifaka infants (reproductive rate=26%) were born, with two of the latter surviving. A total of seven black-and-white ruffed lemurs and 27 diademed sifakas were captured at four disturbed forest sites. Before release in their social units lemurs were checked by vets in a forest that contained natural predators. Released primates were habituated to human presence and monitored with the aid of radio-collars. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  7. A controlled study in 2004–2005 in tropical forest in Sumatra, Indonesia found that all reintroduced Sumatran orangutans Pongo abelii that were released into habitat where the species was absent, 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 were medically screened before being released into habitat. One group was directly released into the forest after a 6-month acclimatization phase at a sanctuary. Another group of individuals was kept in semi-free conditions for 7-9 months prior to release and allowed to overnight in the enclosure. Staff members guided the latter to the forest on a daily basis. Supplementary food was provided regularly. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  8. A before-and-after trial in 2009–2010 in South Africa found that more than half of captive, wild-born vervet monkeys Chlorocebus aethiops that were reintroduced into habitat where the species was absent alongside other interventions, survived for at least six months after release. Three (19%) individuals were reported dead. Of these, two were killed by predators and one by domestic hunting dogs Canis lupus familiaris. Four individuals (25%) went missing. One infant was born two weeks after release. The species was absent from the area of reintroduction. Monkeys were introduced as one troop of 16 individuals. To acclimatize, they spent one day in a release enclosure (49 m2). Monkeys were provided supplementary food twice per day for two weeks and once per day for a further three weeks. The release site was a protected area. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  9. 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.

    Study and other actions tested
  10. A site comparison in 2008–2012 in two forest sites in South Vietnam found that several pygmy slow lorises Nycticebus pygmaeus that were released into habitat where the species was absent, along with eight other interventions, survived for at least two months. Four of eight lorises survived for at least two months after release, whereas the remaining lorises either died or their radio-collar signal was lost at an early stage after release. Both release sites were protected and predators were present. Lorises were released during the wet season after they had undergone a 6-week quarantine, veterinary screens and treatment for parasites. Lorises were kept in a cage for between two days and 2 months, and were supplemented with food for between seven and 30 days. Bodies of dead animals were examined to determine the cause of death. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  11. A site comparison in 2008–2012 in mosaic forest at two sites in South Vietnam found that all pygmy slow lorises Nycticebus pygmaeus that were released into habitat where the species was absent along with other interventions, either died or disappeared. All five lorises either died or their radio-collar signal was lost soon after release. Wild lorises were absent or had very low numbers at the sites. All lorises were quarantined for 6-weeks, were screened by vets and treated for parasites. Individual lorises were released alone. Three lorises were released during the dry season. Another two individuals were held in a semi-wild enclosure for one month to foster behaviour that would aid their survival in the wild. The latter were released during the wet season. Bodies of dead animals were examined to determine their cause of death. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  12. A before-and-after trial in 2008–2010 in a tropical forest in Gabon found that the majority of western lowland gorillas Gorilla gorilla gorilla that were reintroduced into habitat where the species was absent, along with ten other interventions, survived for at least nine months. Four out of five (80%) juvenile gorillas survived for at least nine months after release. Before release gorillas were allowed to adapt to local habitat conditions. Three captive-bred and two orphaned wild born individuals were reintroduced as a group into habitat with predators. Gorillas 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.

    Study and other actions tested
Please cite as:

Junker, J., Kühl, H.S., Orth, L., Smith, R.K., Petrovan, S.O. & Sutherland, W.J. (2019) Primate conservation. Pages 439-491 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Primate Conservation

This Action forms part of the Action Synopsis:

Primate Conservation
Primate Conservation

Primate Conservation - Published 2017

Primate Synopsis

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