Ensure that researchers/tourists are up-to-date with vaccinations and healthy

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

Study locations

Key messages

  • One controlled study in Malaysia found that a population of reintroduced orangutans decreased by 33% over 33 years despite staff and volunteers having received medical checks, alongside other interventions.
  • One before-and-after study in Rwanda, Uganda and Congo found that mountain gorilla numbers increased by 168% over 41 years while sick/unwell researchers and visitors were not allowed to visit gorillas, 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 controlled study in 1967-2004 in tropical forest in Kabili-Sepilok Forest Reserve, Malaysia found that rehabilitated and reintroduced orangutans Pongo pygmaeus morio decreased by 33% over 33 years (1964-1997), although staff and volunteers received medical checks to avoid disease transmission alongside eight other interventions. In addition, 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. 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 daily provided supplementary food from 2-7 feeding platforms. Individuals underwent in-depth veterinary checks and were kept in quarantine for 90 days before release into the reserve, in which other rehabilitated orangutans lived. Sick or injured individuals were captured and treated. 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.

    Study and other actions tested
  2. A controlled, before-and-after study in 1967-2008 in tropical montane forest in Volcanoes-, Mgahinga-, and Virunga National Parks in Rwanda, Uganda, and the Democratic Republic of Congo found that the mountain gorilla Gorilla beringei beringei population that was regularly visited by healthy tourists and researchers alongside ten other interventions, increased in size over time. Annual population growth was 4.1%, resulting in an overall population increase of 168% over 41 years. No statistical tests were carried out to determine whether this increase was significant. Visitors/researchers were asked to report if they were not feeling well and were not allowed to visit the gorillas if they felt sick. As part of the ecotourism- and research programmes, gorillas were habituated to human presence, where visitors/researchers had to follow strict health procedures; these included keeping a safety distance to the gorillas, wearing face-masks, spending only a limited amount of time with gorilla groups, disinfecting visitor’s/researcher’s clothes, boots etc. The population was continuously monitored by vets and individuals received medical treatment if necessary. When gorillas died, their cause of death was examined. The study only tests for the effect of veterinary interventions, but does not distinguish between the effects of the other 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

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

What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

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