Wild orangutans (Pongo spp.) rescued from human-wildlife conflict must be adequately rehabilitated before being returned to the wild. It is essential that released orangutans are able to cope with stressful challenges such as food scarcity, navigating unfamiliar environments, and regaining independence from human support. Although practical skills are taught to orangutans in rehabilitation centres, post-release survival rates are low. Psychological resilience, or the ability to ‘bounce back’ from stress, may be a key missing piece of the puzzle. However, there is very little knowledge about species-appropriate interventions which could help captive orangutans increase resilience to stress. This scoping review summarises and critically analyses existing human and non-human animal resilience literature and provides suggestions for the development of interventions for orangutans in rehabilitation. Three scientific databases were searched in 2021 and 2023, resulting in 63 human studies and 266 non-human animal studies. The first section brings together human resilience interventions, identifying common themes and assessing the applicability of human interventions to orangutans in rehabilitation. The second section groups animal interventions into categories of direct stress, separation stress, environmental conditions, social stress, and exercise. In each category, interventions are critically analysed to evaluate their potential for orangutans in rehabilitation. The results show that mild and manageable forms of intervention have the greatest potential benefit with the least amount of risk. The study concludes by emphasising the need for further investigation and experimentation, to develop appropriate interventions and measure their effect on the post-release survival rate of orangutans.

The attitudes of experts towards the husbandry of captive Great Apes was sought in order to gain a greater understanding of the potential importance of different features of the captive environment that may be critical in maintaining a high standard of welfare. Following initial consultation with the convener of the Primate Taxon Advisory Group of the Australasian Regional Association of Zoological Parks and Aquaria, 17 husbandry attributes, such as social structure of the group, enclosure size and staff qualifications, each with two to four levels (ie husbandry scenarios) of possible provision in an enclosure were identified and described. An online survey using Adaptive Conjoint Analysis was distributed internationally to relevant stakeholders: zoo management staff, keepers and education staff, research colony personnel, veterinarians, animal welfare organisation representatives and scientists. A total of 359 respondents completed the survey, and the average importance values for the attributes, and rank order of importance for each of their levels were calculated. Great Ape social structure, enclosure appearance, group size, avoidance provision and enclosure furnishings were considered the most important attributes of captive Great Ape husbandry, whereas feeding interval, staff qualifications, the inclusion of plants within the enclosure, enrichment rotation, and the amount of time an animal spent in an outdoor enclosure were considered of low importance. The order in which these issues were ranked was influenced by the Great Ape species, with physical attributes of the enclosure being rated as more important for orangutans (Pongo pygmaeus) and group social attributes more important for the other species. Stakeholder group had little influence on the ranking of issues. It is concluded that experts provided a consensus view on the importance of husbandry attributes of the different Great Ape species that can be used to evaluate their welfare.

In recognition of the fact that orang-utans (Pongo spp.) are severely threatened, a meeting of orang-utan experts and conservationists, representatives of national and regional governmental and non-governmental organizations, and other stakeholders, was convened in Jakarta, Indonesia, in January 2004. Prior to this meeting we surveyed all large areas for which orang-utan population status was unknown. Compilation of all survey data produced a comprehensive picture of orang-utan distribution on both Borneo and Sumatra. These results indicate that in 2004 there were c. 6,500 P. abelii remaining on Sumatra and at least 54,000 P. pygmaeus on Borneo. Extrapolating to 2008 on the basis of forest loss on both islands suggests the estimate for Borneo could be 10% too high but that for Sumatra is probably still relatively accurate because forest loss in orang-utan habitat has been low during the conflict in Aceh, where most P. abelii occur. When those population sizes are compared to known historical sizes it is clear that the Sumatran orang-utan is in rapid decline, and unless extraordinary efforts are made soon, it could become the first great ape species to go extinct. In contrast, our results indicate there are more and larger populations of Bornean orang-utans than previously known. Although these revised estimates for Borneo are encouraging, forest loss and associated loss of orang-utans are occurring at an alarming rate, and suggest that recent reductions of Bornean orang-utan populations have been far more severe than previously supposed. Nevertheless, although orang-utans on both islands are under threat, we highlight some reasons for cautious optimism for their long-term conservation.