Immature wild orangutans acquire relevant ecological knowledge through sex-specific attentional biases during social learning.

Beatrice Ehmann,Suci Utami Atmoko,Julia Mörchen,Helvi Musdarlia,Caroline Schuppli,Carel P. van Schaik,Maria A. van Noordwijk,Alison M. Ashbury,Frans B. M. de Waal

doi:10.1371/journal.pbio.3001173

Abstract

As a part of growing up, immature orangutans must acquire vast repertoires of skills and knowledge, a process that takes several years of observational social learning and subsequent practice. Adult female and male orangutans show behavioral differences including sex-specific foraging patterns and male-biased dispersal. We investigated how these differing life trajectories affect social interest and emerging ecological knowledge in immatures. We analyzed 15 years of detailed observational data on social learning, associations, and diet repertoires of 50 immatures (16 females and 34 males), from 2 orangutan populations. Specific to the feeding context, we found sex differences in the development of social interest: Throughout the dependency period, immature females direct most of their social attention at their mothers, whereas immature males show an increasing attentional preference for individuals other than their mothers. When attending to non-mother individuals, males show a significant bias toward immigrant individuals and a trend for a bias toward adult males. In contrast, females preferentially attend to neighboring residents. Accordingly, by the end of the dependency period, immature females show a larger dietary overlap with their mothers than do immature males. These results suggest that immature orangutans show attentional biases through which they learn from individuals with the most relevant ecological knowledge. Diversifying their skills and knowledge likely helps males when they move to a new area. In sum, our findings underline the importance of fine-grained social inputs for the acquisition of ecological knowledge and skills in orangutans and likely in other apes as well.

Highlights

In many mammal species, immature individuals acquire subsistence skills through social learning [1,2,3,4,5]
When comparing overall peering rates of immature males and females in the feeding context, we found no differences between the sexes (S1 Fig, GLMMGaussian: PSexMale = 0.997, EstimateSexMale = 0.0002, Std.ErrorSexMale = 0.069; PAge = 0.100, EstimateAge = −0.467, Std.ErrorAge = 0.072; PSiteTuanan < 0.001, EstimateSiteTuanan = −0.370, Std.ErrorSiteTuanan = 0.073, N = 63 peering rates based on 1,094 peering events by the immatures)
We found no differences in overall association rates according to the immatures’ sexes (S2 Fig, GLMMGaussian: PSexMale = 0.360, EstimateSexMale = 0.059, Std.ErrorSexMale = 0.064; PAge = 0.043, EstimateAge = −0.061, Std.ErrorAge = 0.030; PSiteTuanan < 0.001, EstimateSiteTuanan = −0.240, Std.ErrorSiteTuanan = 0.064, N = 119 association rates based on 16,598 observation hours of the immatures)

Summary

Introduction

Immature individuals acquire subsistence skills through social learning [1,2,3,4,5]. Social learning appears to be prominent in the foraging context, as immatures often closely observe competent individuals while feeding and solicit their food or tools [6,7,8,9,10,11,12,13,14,15,16,17]. With respect to who an immature observes, it has been suggested that among socially learning mammals, and among primates, individuals go through 3 main phases of social learning (reviewed by [18]; see [19,20,21,22,23]). Basic subsistence skills are learned from key caregivers (in most cases, mothers). Whether an individual’s impending dispersal, or the absence thereof, affects their attentional preferences and skill acquisition prior to the actual dispersal event, i.e., during the second phase of social learning, remains unexplored

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