Fostering appropriate behaviour to facilitate rehabilitation

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Study locations

Key messages

  • Two before-and-after studies in Brazil found that most reintroduced golden lion tamarins did not survive over 1–7 years, despite being fostered to survive in the wild, alongside other interventions but in one study they reproduced successfully which partly compensated mortality.
  • Two before-and-after studies in Liberia and Congo found that most reintroduced chimpanzees that were fostered to facilitate reintroduction, alongside other interventions, survived over 1-3.5 years. One before-and-after study in Uganda found that a reintroduced chimpanzee repeatedly returned to human settlements despite being fostered to facilitate reintroduction, alongside other interventions.
  • One controlled study in Indonesia found that reintroduced orangutans that were fostered natural behaviour, alongside other interventions, did not act more like wild orangutans than individuals that were not fostered. One study in Indonesia found that reintroduced orangutans that were fostered to facilitate reintroduction, alongside other interventions, fed on fewer plant species and spent more time building nests.
  • One site comparison study in Vietnam found that all reintroduced pygmy slow lorises were assumed dead despite being fostered natural behaviour prior to release, alongside other interventions.

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 before-and-after trial in 1954-1985 in a degraded rain forest in Poço das Antas Reserve, Brazil found that the number of translocated captive-born golden lion tamarins Leontopithecus rosalia that were habituated to humans and fostered to facilitate survival in the wild along with nine other interventions, more than halved within the first year of release. No statistical tests were carried out to determine whether this decrease was significant. Of the 14 individuals released, seven died and two were removed. Three infants were born, one of which died. Eight individuals were released as a family group and six individuals were released as pairs one month later. Tamarins spend an unknown amount of time in 15 x 4.5 x 3 m outside enclosures. The reserve included natural predators. Sick or injured tamarins were captured and treated. Tamarins were supplied with food for 10 months post-release. Artificial nesting boxes, which were hollow logs provided to them during training, were set up in the reserve. 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 1984-1991 in coastal forest in Poço das Antas Reserve, Brazil found that over 60% of the reintroduced golden lion tamarins Leontopithecus rosalia, some of which were trained in behaviours to facilitate survival alongside 14 other interventions, did not survive over seven years. Fifty-eight (64%) out of 91 individuals did not survive in the wild. However, 57 infants were born (reproductive rate=63%), of which 38 (67%) survived. Tamarins were trained in food detection, strength and locomotor ability, and predator detection and avoidance. 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 provided with supplementary food, water and nesting boxes, and allowed to adapt to local conditions before release. Tamarins underwent quarantine, veterinary checks, and were treated for parasites before release. Sick or injured animals were captured treated and re-released. The reserve became officially protected in 1983s. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  3. A before-and-after-trial in 1995 in a tropical forest in Kibale National Park, Uganda found that a female captive, 4-6 year old wild-born chimpanzee Pan troglodytes schweinfurthii that underwent pre-release training with caretakers in the forest before reintroduction into a human-habituated community of wild chimpanzees along with other interventions, repeatedly returned to human settlements after release and was subsequently returned to captivity. Eight days post-release, the chimpanzee left the forest and was returned to the forest. For the following ten days, she travelled, fed, nested and engaged in social activities with the wild community. She increased ranging distance to humans and use of height, and visually monitored humans less regularly. However, she increasingly spent more time alone and was returned to captivity six weeks after being released. During the three weeks of pre-release training in the forest, caretakers initiated progressions (up to 6 km) to reach known food sources, increase her endurance and improve her familiarity with the habitat. The chimpanzee was quarantined before reintroduction and was tested for tuberculosis. Ten community members worked on the project. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  4. A study in 1987-1988 on an island in tropical forest in Liberia, West Africa found that the majority of reintroduced western chimpanzees Pan troglodytes verus, that were fostered behaviour to facilitate reintroduction along with other interventions, survived for at least one year. Seven out of 30 released chimpanzees had difficulties to adjust to the new social environment and were brought back to captivity. Chimpanzees were socialized in naturalistic enclosures and taught to find and process food and water, avoid predators, seek or make shelters, and mate and rear offspring. Chimpanzees underwent pre-release health checks and were allowed to adapt to the local habitat in enclosures. Chimpanzees were released in groups and younger and low-ranking individuals were released earlier to reduce stress. Released individuals were continuously provided with food. Sick and injured animals were temporarily removed for treatment. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  5. 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 chimpanzees Pan troglodytes troglodytes that were fostered behaviour to facilitate survival in the wild along with eight other interventions, 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 diet similar to wild chimpanzees. They also had activity budgets that resembled those of wild conspecifics. No statistical tests were carried out to determine whether these similarities were statistically valid. Orphan chimpanzees were rehabilitated and fostered at a nearby sanctuary and accompanied to the forest to help to aid to recover from capture and create social bonds. Chimpanzees underwent veterinary screens, endoparasite treatments and were vaccinated. Before reintroduction in groups into habitat with low densities of resident wild chimpanzees, they spent 6-9 years on one of three forested islands in the region. Researchers were present on-site and monitored chimpanzees with radio-collars. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  6. A controlled study in 2004-2005 in secondary tropical forest in Bukit Tigapuluh National Park, Indonesia found that reintroduced Sumatran orangutans Pongo abelii that were not fostered natural behaviour along with other interventions, acted more like wild orangutans after release than individuals that had been fostered. The behaviour of the three non-fostered orangutans resembled that of wild orangutans more than that of the five fostered individuals in the way that they built nests, selected food and used the canopy. Non-fostered individuals spent more time interacting socially with previously released orangutans. However, some individuals of the fostered group learned some natural behaviour by watching orangutans that were reintroduced earlier. Individuals in this group were guided daily from night enclosures to the forest and were shown how to handle wild food. They acclimatized to local conditions for 7-9 months before release and were free to overnight in the enclosure. The study does not distinguish between the effects of the different interventions mentioned above.

    Study and other actions tested
  7. A study in the wet season in 2009 in two rainforest patches in the Orangutan Care and Quarantine Centre, Indonesia found that captive orphaned juvenile Bornean orangutans Pongo pygmaeus that were fostered to facilitate reintroduction fed on fewer species and spent less time building nests than wild orangutans. Orphans fed on 72 different wild food species, mainly leaves (18%), fruit (15%), bark (7%), and invertebrates (7%), whereas wild orangutans fed on more than 300 different foods, mainly fruit (70%), bark (20%) and leaves (15%). Orphans spent 3% of their time building nests, which corresponded to half of the time spent by wild orangutans. In addition, orphans most commonly travelled by quadrupedal arboreal locomotion, a form of locomotion similar to that used by wild orangutans in Sumatra. Over a 5-month period, a random sample of 40 male and female juvenile orangutans of varying health was observed during three 5-hour excursions to each one of two nearby forest patches. Individuals were provided a midday feed of rice or fruit.

    Study and other actions tested
  8. A site comparison in 2008-2012 in mosaic forest at two sites in Cat Tien National Park, South Vietnam (8) found that all pygmy slow lorises Nycticebus pygmaeus that were allowed to learn natural behaviours prior to release alongside other interventions, either died or disappeared. All five lorises that were reintroduced died or their radio collar signal was lost at an early stage after release. Two individuals were held in a semi-wild enclosure for one month to foster behaviour aimed at facilitating survival in the wild. The latter were released during the wet season. Three other lorises were released at Cat Tien National Park during the dry season. Monkeys underwent a 6-week quarantine, veterinary screens, and parasite treatment. Lorises were released as multiple individuals into habitat with no resident lorises but with predators. Bodies of dead animals were examined. 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. (2020) Primate Conservation. Pages 431-482 in: W.J. Sutherland, L.V. Dicks, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2020. Open Book Publishers, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

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Primate Conservation

This Action forms part of the Action Synopsis:

Primate Conservation
Primate Conservation

Primate Conservation - Published 2017

Primate Synopsis

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