In an effort to understand orangutan sociality and what benefits might be gained from socializing for a semi-solitary ape, we explore the details of the social lives of the most gregarious orangutan age-sex class - adolescent females. From 1994-2016 adolescent females in Gunung Palung National Park spent 50% of their focal follow days with at least one social association, and 31% of their focal follow time with at least one other independently ranging individual. Adolescent females are the party responsible for initiating their social associations with other age-sex classes 86% of the time. The percentage of approaches performed by adolescent females within dyadic associations is significantly predicted by the age-sex class of their social partner (F=4.086, p=0.02), with adolescents performing most of the approaches in associations with adult females (70%), and a more mutual responsibility for proximity maintenance when they associate with flanged males (46%) or unflanged males (56%). These findings, in combination with rates of agonistic interactions with adult females and affiliative behaviors with unflanged males, indicate that adolescent females actively seek social opportunities with all age-sex classes, but the benefits and risks associated with socializing vary based on the age-sex of their social partners. We discuss the importance of sociality at this life stage for orangutans, and the potential that there are meaningful social bonds beyond the mother-offspring dyad in the wild.
Funders: BU GRAF, NSF (BCS-1638823, BCS-0936199, 9414388), National Geographic Society, US Fish and Wildlife (F15AP00812, F12AP00369, 98210-8-G661), Leakey Foundation, Disney Wildlife Conservation Fund, Wenner-Gren, Nacey-Maggioncalda Foundation, Conservation, Food and Health Foundation
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Orangutan Nesting Behavior in Gunung Palung National Park, West Kalimantan, Indonesia
Nesting behavior is unique to the great apes
among primates and has wide ranging implications
for understanding socioecology and
conservation. While much is known about
nesting in gorillas, chimpanzees, and some orangutan
populations living in disturbed forest and
peat swamp, the nesting behavior of orangutans
living in primary forest is poorly understood.
We studied the nesting behavior of Bornean
orangutans (Pongo pygmaeus wurmbii) in
Gunung Palung National Park, West Kalimantan,
Indonesia, using observations of 4,526 nesting
events collected between October 1994 and
September 2018, testing hypotheses about nest
height. We found a significant effect of age/sex
on nest height (F(3)=106.1, p<0.001). Post-hoc
comparisons (adjusted α-level= 0.008) showed
that flanged males nested significantly lower
than all other age/sex classes (p<0.001) while
females nested significantly lower than juveniles
and unflanged males (p<0.001). Flanged males
and females tended to nest lower in the canopy
when alone than in the presence of other orangutans
(males: F(3)=24.25, p<0.001; females:
F(3)=5.83, p=0.001). Our results help demonstrate
that across forest types, flanged male
orangutans prefer to nest lower in the canopy
while all other age- and sex-classes prefer higher
canopy positions for nesting. Furthermore, our
finding that solitary individuals nest lower than
individuals near other orangutans suggests that
nesting higher in the canopy may allow individuals
to space their nests optimally when in
proximity of other orangutans. These results
have significant conservation implications, as
logging and deforestation fundamentally change
the forest structure, disrupting the canopy and
making preferred nesting locations unavailable.
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- NSF-PAR ID:
- 10110436
- Date Published:
- Journal Name:
- American journal of physical anthropology
- Volume:
- 168
- Issue:
- S68
- ISSN:
- 0002-9483
- Page Range / eLocation ID:
- 30
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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In an effort to understand orangutan sociality and the benefits of socializing for a semi-solitary ape, we explore the social lives of the most gregarious orangutan age-sex class - adolescent females. From 1994-2016 adolescent females in Gunung Palung National Park had a social encounter on 50% of their follow days, spending 31% of their time in the company of others. Adolescent females were responsible for initiating social parties (coming within 50 meters) with other age-sex classes 86% of the time. Once they were in a social party, the percentage of approaches (decreases in distance between individuals) performed by adolescent females was significantly predicted by the age-sex class of their social partner (F=4.086, p=0.02). Adolescent females performed most of the approaches when they associated with adult females (70%), while approaches were more equal when they associated with flanged males (46% performed by adolescent females) or unflanged males (56% performed by adolescent females). These findings, in combination with higher rates of agonistic interactions between adolescent and adult females and higher rates of affiliative behaviors between adolescent females and unflanged males, indicate that adolescent females actively seek social opportunities with all age-sex classes, but the benefits and risks associated with socializing vary based on the age-sex of their social partners. We argue that sociality is important during adolescence for female orangutans because they must establish themselves in the social landscape, and must seek social learning opportunities. Finally, we consider the adaptive significance of meaningful social bonds for a semi-solitary, sexually coercive ape.more » « less
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