Future coexistence with great apes will require major changes to policy and practice.

The great apes-bonobos, chimpanzees, gorillas and orangutans-are critically threatened by human activities. We have destroyed their habitats, hunted them and transmitted fatal diseases to them. Yet we also conduct research on them, try to protect them and live alongside them. They are endangered, and time is running out. Here we outline what must be done to ensure that future generations continue to share this planet with great apes. We urge dialogue with those who live with great apes and interact with them often. We advocate conservation plans that acknowledge the realities of climate change, economic drivers and population growth. We encourage researchers to use technology to minimize risks to great apes. Our proposals will require substantial investment, and we identify ways to generate these funds. We conclude with a discussion of how field researchers might alter their work to protect our closest living relatives more effectively.

The Development of Feeding Competence in Rehabilitant Orphaned Orangutans and How to Measure It.

For critically endangered species, restorative conservation becomes increasingly important. Successful re-introduction of rescued wild orangutan orphans requires rehabilitation mimicking maternal rearing in the wild. Feeding competence-what to eat, where and when to find food-needs to be learned before re-introduction. We observed seven orphans (2-10 years old) for a period of 3 years during their rehabilitation at the Yayasan Jejak Pulang forest school. Of the 111 plant genera eaten by the orphans, 92 percent were known orangutan food plants. Five plant genera were eaten by all orphans in over 90 percent of the months within the observation period. The Fruit Availability Index (FAI) was used to predict which parts of a plant were consumed by the orphans. We found that the orphans ate primarily fruit when the FAI was high, but consumed more young leaves, cambium, and pith when FAI was low. Thus, the orphans exhibited food choices very similar to mature wild orangutans and appropriate to forest productivity. The orphans' acquisition of feeding competence was facilitated by their immersion into a natural forest environment in combination with possibilities for observational learning from conspecifics as well as caregivers modelling food processing and consumption.

Learning to Be an Orangutan-Implications of Life History for Orangutan Rehabilitation.

Orangutans depend on social learning for the acquisition of survival skills. The development of skills is not usually assessed in rescued orphans' pre-release. We collected data of seven orphans over an 18-months-period to monitor the progress of ontogenetic changes. The orphans, 1.5-9 years old, were immersed in a natural forest environment with human surrogate mothers and other orphans. Social interactions deviated significantly from those of wild mother-reared immatures. Infants spent more time playing socially with peers, at the expense of resting and solitary play. Infants were also more often and at an earlier age distant from their human surrogate mothers than wild immatures are from their biological mothers. We found important changes towards an orangutan-typical lifestyle in 4- to 7-year-old orphans, corresponding to the weaning age in maternally reared immatures. The older orphans spent less time interacting with human surrogate mothers or peers, started to use the canopy more than lower forest strata and began to sleep in nests in the forest. Their time budgets resembled those of wild adults. In conclusion, juvenile orphans can develop capacities that qualify them as candidates for release back into natural habitat when protected from humanising influences and immersed in a species-typical environment.

Early maternal loss affects social integration of chimpanzees throughout their lifetime.

The long-term effects of early adverse experiences on later psychosocial functioning are well described in humans, but sparsely documented for chimpanzees. In our earlier studies, we investigated the effects of maternal and social deprivation on three groups of ex-laboratory chimpanzees who experienced either an early or later onset of long-term deprivation. Here we expand our research by adding data on subjects that came from two stable zoo groups. The groups comprised of early maternally deprived wild-caught chimpanzees and non-deprived zoo-born chimpanzees. We found that compared to zoo chimpanzees, ex-laboratory chimpanzees were more restricted regarding their association partners in the newly formed groups, but not during their second year of group-life, indicating that social stability has an important influence on the toleration of association partners close-by. Social grooming activity, however, was impaired in early long-term deprived ex-laboratory chimpanzees as well as in early maternally deprived zoo chimpanzees compared to non-deprived zoo chimpanzees. Thus, we conclude that early maternal loss has lifelong effects on the social integration of chimpanzees which becomes evident in their grooming networks. Although the retrospective nature of our study prevents a clear causal explanation, our results are of importance for understanding the development of social competence in chimpanzees.

Long-Term Evaluation of Abnormal Behavior in Adult Ex-laboratory Chimpanzees (Pan troglodytes) Following Re-socialization.

Adverse rearing conditions are considered a major factor in the development of abnormal behavior. We investigated the overall levels, the prevalence and the diversity of abnormal behavior of 18 adult former laboratory chimpanzees, who spent about 20 years single caged, over a two-year period following re-socialization. According to the onset of deprivation, the individuals were classified as early deprived (EDs, mean: 1.2 years) or late deprived (LDs, mean: 3.6 years). The results are based on 187.5 hours of scan sampling distributed over three sample periods: subsequent to re-socialization and during the first and second year of group-living. While the overall levels and the diversity of abnormal behavior remained stable over time in this study population, the amplifying effects of age at onset of deprivation became apparent as the overall levels of abnormal behavior of EDs were far above those of LDs in the first and second year of group-living, but not immediately after re-socialization. The most prevalent abnormal behaviors, including eating disorders and self-directed behaviors, however, varied in their occurrence within subjects across the periods. Most important, the significance of social companionship became obvious as the most severe forms of abnormal behavior, such as dissociative and self-injurious behaviors declined.

Social competence of adult chimpanzees (Pan troglodytes) with severe deprivation history: I. An individual approach.

Early social deprivation in highly social mammals interferes with their varying needs for security and stimulation. Toleration of social stimulation was studied in 18 adult ex-laboratory chimpanzees, who had been deprived for 16 to 27 years, during their 1st year after resocialization into 1 of 3 social groups. For this, a model of social competence was developed with 5 grades of social stimulation. The chimpanzees were classified as either early deprived (EDs; M = 1.2 years) or late deprived (LDs; M = 3.6 years) according to their age at entering the laboratory. EDs did not differ significantly from LD chimpanzees in the first 3 grades of social stimulation (i.e., the toleration of stationary vicinity, initiation of brief sociopositive contacts and gentle social play). LDs, however, clearly exceeded EDs in the 4th and 5th grade of social stimulation (i.e., their engagement in allogrooming and their toleration of passive close proximity). Furthermore, LDs showed greater social initiative in changing a social situation and had more expanded grooming networks compared with EDs. Moreover, in LDs and ED females, but not in ED males, toleration of stationary vicinity increased from the 1st to the 2nd year of group living.

Skill mastery inhibits adoption of observed alternative solutions among chimpanzees (Pan troglodytes).

Geographic variation in socially transmitted skills and signals, similar to human culture, has been well documented for great apes. The rules governing the adoption of novel behaviours, however, are still largely unknown. We conducted an innovation-and-transmission experiment with two groups of chimpanzees living at hopE Primate Sanctuary Gänserndorf, Austria, presenting a board on which food had to be manoeuvred around obstacles to be acquired. Most chimpanzees used sticks to acquire the food, but five adults independently invented a novel technique, rattling, which was subsequently tested by almost all group members. However, individuals who had become proficient with sticks were reluctant to switch to rattling, despite it being more efficient. Similarly, after rattling was prevented, rattle specialists kept trying to rattle and made no attempt to use the stick technique, despite their knowledge about its existence. We conclude that innovators stimulate others to experiment with the solutions they display, but that chimpanzees are nevertheless conservative; mastery of a skill inhibits further exploration, and hence adoption of alternative techniques even if these are more efficient. Consequently, conformity among group members should not be expected in great apes when individuals develop proficiency at different techniques. Conservatism thus joins conformity as a mechanism to bring about cultural uniformity and stability.

Differential onset of infantile deprivation produces distinctive long-term effects in adult ex-laboratory chimpanzees (Pan troglodytes).

Maternal or social deprivation during early infancy inevitably produces social deficiencies in juvenile chimpanzees. Hypothesizing such deficiencies to persist into adulthood (a), and, as in humans, a sensitive period in early infancy for attachment formation (b), we predicted and found behavioral differences in resocialized adult ex-laboratory chimpanzees after about 20 years of solitary confinement depending on their age at onset of deprivation: early deprived (ED; mean: 1.2 years) chimpanzees engaged significantly less in social interactions, spent less time associated, and showed more nonsocial idiosyncrasies than did late deprived (LD; mean: 3.6 years) chimpanzees. In addition to these individual attributes relational qualities, specifically the combination of ED and LD chimpanzees within social groups, have an impact on social recovery. LDs can best exploit their social potential in the company of other LDs and EDs tend to stagnate in their recovery when socialized with other EDs.

Rehabilitation of research chimpanzees: stress and coping after long-term isolation.

We report on the permanent retirement of chimpanzees from biomedical research and on resocialization after long-term social isolation. Our aim was to investigate to what extent behavioral and endocrine measures of stress in deprived laboratory chimpanzees can be improved by a more species-typical social life style. Personality in terms of novelty responses, social dominance after resocialization and hormonal stress susceptibility were affected by the onset of maternal separation of infant chimpanzees and duration of deprivation. Chimpanzees, who were separated from their mothers at a younger age and kept in isolation for more years appeared to be more timid personalities, less socially active, less dominant and more susceptible to stress, as compared to chimpanzees with a less severe deprivation history. However, permanent retirement from biomedical research in combination with therapeutic resocialization maximizing chimpanzees' situation control resulted in reduced fecal cortisol metabolite levels. Our results indicate that chimpanzees can recover from severe social deprivation, and may experience resocialization as less stressful than solitary housing.

Psychopathology in great apes: concepts, treatment options and possible homologies to human psychiatric disorders.

Many captive great apes show gross behavioral abnormalities such as stereotypies, self-mutilation, inappropriate aggression, fear or withdrawal, which impede attempts to integrate these animals in existing or new social groups. These abnormal behaviors resemble symptoms associated with psychiatric disorders in humans such as depression, anxiety disorders, eating disorders, and post-traumatic stress disorder. Due to the outstanding importance of social interaction and the prolonged period of infantile and juvenile dependence, early separation of infants from their mothers and other adverse rearing conditions, solitary housing, and sensory deprivation are among the major albeit non-specific sources of psychopathology in apes. In contrast to the wealth of research in monkeys, psychopathology in apes has been under-studied, and only a few studies have examined how to alleviate abnormal behavior in captive apes. Recent studies have shown that the enrichment of living conditions and behavioral treatment (conditioning) may ameliorate some pathological features, and careful familiarization with novel physical and social environments can help re-socialize behaviorally disturbed animals, but usually not to the extent of successful mating and raising offspring. The possibility of psychopharmacological treatment of the most severe disturbed animal patients has only been reluctantly considered, but a few case reports have revealed encouraging results. This article proposes the need to expand research into ape psychopathology, which would require an essentially interdisciplinary approach of primatology and psychiatry, ultimately to the benefit of both.