Why do orangutans leave the trees? Terrestrial behavior among wild Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan, Central Kalimantan

Abstract. Fauzi F, Suemarno, Afandhi A, Leksono AS. 2020. Nesting behavior of Bornean immature Orangutan (Pongo pygmaeus wurmbii) in Nyaru Menteng Arboretum School, Palangka Raya, Central Kalimantan, Indonesia. Biodiversitas 21: 2172-2179. This research aimed at analyzing the nesting behavior of Bornean Orangutan (Pongo pygmaeus wurmbii) in Nyaru Menteng Arboretum, Palangka Raya, Central Kalimantan, Indonesia. The objects of observation were the immature orangutan nest, and the type of nest tree. The purposive sampling technique was used because not all immature Orangutan could make a nest. The Focal animal sampling method was used to determine the daily behavior and nets building activity. It involved observing and recording the behavior of five young Orangutans over a certain period of time and analyzing the nest made. The results of the study established that the daily activity of immature Orangutan on an average sequentially ranges from feeding 17.18%, moving 23.92%, resting 26.34%, and social behavior 32.57%. The process of making a nest begins with finding a suitable branch, bending and breaking twigs, and then arranging the twigs and leaves as a mattress. The duration of building a nest was 5.00 to 6.44 minutes, the preferred nest tree was Palaquium xanthochymum and Shorea spp., and the direction of the nest more facing west.

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The development and maintenance of sex differences in dietary breadth and complexity in Bornean orangutans

Behavioral Ecology and Sociobiology ◽

10.1007/s00265-021-03014-3 ◽

2021 ◽

Vol 75 (5) ◽

Author(s):

Caroline Schuppli ◽

S. Suci Utami Atmoko ◽

Erin R. Vogel ◽

Carel P. van Schaik ◽

Maria A. van Noordwijk

Keyword(s):

Sex Differences ◽

Foraging Behavior ◽

Role Models ◽

Pongo Pygmaeus ◽

Data Set ◽

Dietary Breadth ◽

Adult Females ◽

Pongo Pygmaeus Wurmbii ◽

Males And Females ◽

Bornean Orangutans

Abstract Orangutans show a pronounced sexual dimorphism, with flanged males (i.e., males with fully grown secondary sexual characteristics) reaching twice the size of adult females. Furthermore, adult orangutans show sex-specific dispersal and activity patterns. This study investigates sex differences in adult foraging behavior and sheds light on how these differences develop in immatures. We analyzed 11 years of feeding data on ten adult female, seven flanged male, and 14 immature Bornean orangutans (Pongo pygmaeus wurmbii) at Tuanan in Central Kalimantan, Indonesia. We found that the diets of the adult females were significantly broader and required more processing steps before ingestion than the diets of flanged males. We also found evidence for a similar difference in overall diet repertoire sizes. For the immatures, we found that whereas females reached 100% of their mothers’ diet spectrum size by the age of weaning, males reached only around 80%. From the age of 4 years on (i.e., years before being weaned) females had significantly broader daily diets than males. We found no difference in daily or overall diet processing intensity of immature males and females but found preliminary evidence that immature males included fewer items of their mother’s diet in their own diets that were processing-intensive. Overall, our results suggest that by eating a broader variety and more complex to process food items, female orangutans go to greater lengths to achieve a balanced diet than males do. These behavioral differences are not just apparent in adult foraging behavior but also reflected in immature development from an early age on. Significance Statement In many species, males and females have different nutritional needs and are thus expected to show sex-specific foraging behavior. Sex differences in several aspects of foraging behavior have been found in various species, but it remains largely unclear when and how those develop during ontogeny, which is especially relevant for long-lived altricial species that learn foraging skills over many years. In our study, we analyzed a cross-sectional and longitudinal data set containing more than 750,000 feeding events of adult and immature Bornean orangutans (Pongo pygmaeus wurmbii). We found that adult females had significantly broader and more complex diets than males. We also found that these differences started to develop during infancy, suggesting that immature orangutans prepare for their sex-specific foraging niches long before those become physiologically relevant while they are still in constant association with their mothers and before being frequently exposed to other role models.

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