Observational learning in orangutan cultural transmission chains

Field reports suggest that orangutans acquire local traditions by observing neighbouring conspecifics. However, there is little direct evidence of social learning to support this conclusion. The present study investigated whether orangutans would learn a novel foraging method through observation of a conspecific in a diffusion-chain paradigm testing for the spread of the behaviour. A foraging box with two possible methods for extracting food was used to investigate the transmission of a foraging tradition among zoo-living subjects. In a socially housed group of five orangutans, the dominant male was trained to use one technique exclusively to retrieve food. He then performed this technique in the presence of another group member, who was then allowed to forage. After several trials, the observer became the model for the next individual. A second experimental group of six individuals was introduced to the alternative method. The model-seeded technique was successfully transmitted along both experimental chains, with significant preferences for the model method. These results are consistent with claims for social transmission of foraging methods in wild orangutans.     

Aspects of dental development in the orangutan prior to eruption of the permanent dentition

In spite of a resurgence of interest in the interpretation of the sequences of dental development and eruption in various Plio-Pleistocene hominoids as being either “modern human” or “ape-like,” the body of comparative material on the extant hominoids remains deficient in critical areas. In concert with recent attempts to rectify this situation, we present the results of our studies on dental morphogenesis in the orangutan. We have focused on the growth and eruption of the deciduous dentition as well as early stages of permanent tooth formation and have found that 1) many permanent teeth develop earlier than was thought, 2) differences exist between development in the upper and in the lower jaw, and 3) states of tooth formation can vary significantly among individuals of similar chronological age or tooth eruption status.     

North American orangutan species survival plan: Current status and progress in the 1980s

The SSP program for orangutan (Pongo pygmaeus ssp.) was initiated in 1982. Since that time, the Propagation Group has dealt with issues related to improving captive management of the species. Prior to 1982, most orangutans in North America were managed as a single species, though a number of institutions did house their Bornean and Sumatran specimens separately. However, the determination of race at that time was made largely on the basis of physical appearance, a method subsequently proven imprecise. A major achievement of the SSP has been the refinement of orangutan subspecies determination; SSP-sponsored karotyping has determined, on a chromosomal level, the true subspecies of virtually every orangutan managed by the SSP. The validity of these results has been confirmed by recent fieldwork, also completed under the auspices of the SSP. Since 1985, as a result of these captive and field data, the SSP has held to the policy that subspecific hybrid orangutans should not be produced; to that end, there is a moratorium on the breeding of hybrid animals. Another significant step taken by the SSP group is the completion of the sophisticated demographic and genetic analyses, leading to the development of a Masterplan for this species and its captive management. Goals for the near future include refinement of the Masterplan analyses and publication of a new international studbook for the species.     

Orangutans' color preference for food items

The effects of the addition of color to a dry primate diet on the feeding behavior of orangutans were studied. Purina Monkey Chow was dipped in food coloring (red, green, blue, orange). Colored and plain chow was offered to the subjects, three adults, and two juveniles. Time to eat or lose interest in feeding, quantity, and color of pieces of chow handled and eaten were recorded for each group. The juveniles' consumption of chow increased when offered colored chow, and adults required less time to consume their food. One juvenile showed a significant preference for red monkey chow.     

Sexual resurgence and possible induction of reproductive synchrony in a captive group of orangutans

In April 1985, a 22-year-old group-living female orangutan gave birth to her second infant, marking an interbirth interval of 12 years, 2 months. The timing and patterning of sexual activity displayed by the group of two females and one male over a 3-year period were analyzed to identify variables that might account for this female's sexual resurgence. Variables considered were (1) movement to a new habitat, (2) opening of a vaginal stricture, (3) addition of a second female to the group, (4) male sexual resurgence, and (5) copulatory synchrony. None of these variables alone could account for the resurgence of fertility, although several of them account for the increase in copulatory frequency. This suggests that a combination of factors may be operating, including the induction of fertility via the presence of another cycling female. This induction effect has been described for rhesus macaques, and since this orangutan group meets the conditions necessary for such an induction effect, it is offered as another possible variable influencing fertility. Indices of pregnancy determination, as they relate to gestation lengths and prematurity of infants, also are evaluated and compared.     

Variables that influence the activity of captive orangutans

It is well known that the environment significantly influences the behavior of captive animals. However, the specific nature of the cues that promote speciestypical behavior patterns is not usually known. This study extends an earlier investigation by Wilson (Zoo Biology 1: 201–209, 1982). The objective was to identify and quantify specific environmental components that influence activity levels in orangutans. Six enclosure variables were quantified, and activity levels measured, for 29 orangutans housed in nine zoological parks. Multiple regression analysis indicated that the combination of the number of animals, amount of usable surface area, number of movable objects, and enclosure volume was the best predictor of activity levels, accounting for 58% of the variance in activity levels. It was concluded that the provision of large enclosures, containing large numbers of movable objects and providing social opportunities, would promote higher levels of activity in captive orangutans. © 1992 Wiley-Liss, Inc.     

Airsacculitis in fourteen juvenile southern Bornean orangutans (Pongo pygmaeus wurmbii)

BACKGROUND: Airsacculitis is a clinical condition which has been reported in a range of primates species, including orangutans. METHODS: This report describes the occurence and management of airsacculitis in fourteen juvenile Southern Bornean orangutans (Pongo pygmaeus wurmbii) that presented beween January 1st 1999 and January 31st 2001 at the Orangutan Care Center and Quarantine (OCC&Q), Kalimantan Tengah, Indonesia (S 2 degrees 43' 49.2"; E 111 degrees 38' 54.2"). Details of the signalment, clinical history, presenting clinical signs, clinicopathological findings and bacterial isolates in each case were reviewed. RESULTS: Cough, halitosis and nasal discharge were the most frequently observed clinical signs. A range of Gram-negative bacteria were isolated from infected air sacs, including Pseudomonas sp., Enterobacter sp. and Klebsiella pneumoniae. A simple drainage and lavage technique was used in cases where surgical intervention was indicated, in combination with local and systemic antibiotic therapy. CONCLUSIONS: The importance of early diagnosis, prompt management and antibiotic selection, based on bacterial culture and sensitivity profiles, is outlined.     

The evolution of large body size in orangutans: A model for hominoid divergence

Recent Miocene fossil discoveries of large hominoids resemble orangutans. Since the evolution of large body size was functionally related to a powerful masticatory system in Miocene ape radiations, a better understanding of adaptations in extant orangutans will be informative of hominoid evolution. It is suggested here, based on the behavioral ecology of extant orangutans, that foraging energetics and large body size are tied to a dietary shift that provided access to and utilization of resources not generally available to other primates.     

Control of intragroup aggression by a captive male orangutan

An adult male orangutan, housed with two adult females, intervened in female-female aggressive interactions at least seven times over a 4.5-year period. Five of these seven episodes involved multiple interventions rather than a single act. One series of interventions was directly observed during an ongoing study of spatial relationships, and six other episodes were described in the zoo records. The intervention that was observed directly began with one female displacing the other, after which the male located himself between the two females. He remained nearer the displaced female than he did to the other female. These seven episodes demonstrate the male's mediation and regulation of intragroup aggression. Whereas the opportunities for the control of aggression are limited in the wild, the conditions of captivity likely allowed for the expression of this behavior pattern.