Previous studies showed that it takes immature orangutans around 8 years to establish the full extent of their diet repertoires 6.
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Most of these food items require a distinctive combination of manual and oral processing steps before they can be ingested 6, 7 with some items even requiring the use of stick tools for their extraction 8.
Immature orangutans must acquire a broad range of ecological skills to become self-sufficient, which includes learning to locate, identify and process 4 more than 200 different food items (i.e., the combination of the species and the part of the species that is eaten) 5. Hence, because they cannot resort to the knowledge of association partners, to be able to be weaned immature orangutans must have their skills sufficiently in place before leaving their mother 2, 3. The long nutritional dependence is likely a result of a combination of factors, including the orangutan’s semi-solitary life-style (solitary life-style hypothesis 2, 3): immature orangutans start ranging independently from their mothers shortly after weaning 2, 3 and from that point onward spend between 60 and 90 percent of their time on their own 3. Orangutans mothers get pregnant only after they have weaned their previous offspring, which leads to very long interbirth intervals and thus slow reproductive rates 1. With weaning at the age of 6.5–9 years, orangutans ( Pongo spp.) show one of the longest periods of nutritional dependence in mammals 1. We conclude that orangutan mothers have a more active role in the skill acquisition of their offspring than previously thought. Furthermore, mothers flexibly adjust their behaviour in a way that likely facilitates their offspring’s skill acquisition. Our results indicate that immature Sumatran orangutans use food solicitation to acquire feeding skills. Mothers were more likely to share complex items and showed the highest likelihoods of sharing around the age at which immatures are learning most of their feeding skills. We found that solicitation rates decreased with increasing age of the immatures and increased with increasing processing complexity of the food item. To investigate the role of food solicitation and the role of the mother in immatures’ foraging skill acquisition, we analysed 1390 food solicitation events between 21 immature Sumatran orangutans ( Pongo abelii) and their mothers, collected over 13 years at the Suaq Balimbing orangutan population. Food solicitations are potential means to social learning which, because of their interactive nature, allow to investigate the degree of active involvement of the mother. From a fitness point of view, it may be adaptive for mothers to facilitate their offspring’s skill acquisition to make them reach nutritional independence faster. So far, it has remained uninvestigated to what extent orangutan mothers are actively involved in this learning process.
Immature orangutans acquire their feeding skills over several years, via social and independent learning.