Newswise — Orangutans demonstrate a unique level of dependence on their mothers, surpassing that of any other non-human animal. They rely on their mothers for an extended period, nursing until they reach at least six years of age and cohabiting for up to an additional three years. During this time, they acquire essential skills related to foraging, selecting, and processing the diverse range of foods they consume. However, when orangutans venture away from their native habitats to regions with different available food sources, they face the challenge of determining what to eat and how to consume it. To address this dilemma, an international team of researchers has discovered that such migrating orangutans employ a strategy of observation and emulation, adopting the behavior of local individuals.
According to Julia Mörchen, the study's lead author and a doctoral student at the Max Planck Institute for Evolutionary Anthropology and Leipzig University in Germany, "Our findings provide evidence that male orangutans who have migrated to new areas utilize observational social learning to acquire new ecological knowledge from local individuals. These migrants not only learn about food sources and preferences from the locals but also continue to learn the methods of processing these unfamiliar foods."
Mörchen and her colleagues demonstrated that migrant male orangutans acquire this information through a behavior known as "peering." This involves the intensive observation of a role model for a minimum of five seconds and from a distance of no more than two meters. Peering orangutans typically position themselves facing the role model and exhibit signs of imitating their actions through head movements, indicating a high level of attentive interest.
After reaching independence, male orangutans often embark on migration to new areas, whereas females tend to establish their territories near their place of birth. The specifics of how far and where exactly male orangutans disperse still remain unknown. However, informed speculations can be made based on genetic data and observations of orangutans overcoming physical barriers such as rivers and mountains. These suggest that male orangutans engage in long-distance dispersal, potentially spanning tens of kilometers, during their migration.
According to Mörchen, "This implies that during migration, males are likely to encounter various habitat types and experience diverse faunal compositions, particularly when traversing habitats at different altitudes. Over evolutionary time, the ability to adapt swiftly to new environments by acquiring crucial information from local individuals likely conferred a survival advantage. Consequently, this ability is likely ancestral in our hominin lineage, dating back at least 12 to 14 million years to our last common ancestor with orangutans."
The researchers observed male orangutans engaging in "peering" on 534 occasions, with this behavior observed in 207 (5.2%) of these social interactions. In the Suaq Balimbing population, males predominantly peered at local females, followed by local juveniles, and least often at adult males. In contrast, the less socially inclined population of Tuanan displayed the opposite pattern, with males peering most frequently at adult males, followed by immature orangutans, and least often at adult females. In the Tuanan population, migrant males may have limited opportunities to observe local females, as females tend to avoid prolonged associations with them. Subsequently, the migrant males applied what they had learned through peering by interacting more frequently with the food items observed during the peering process, putting their acquired knowledge into practice.
Dr. Anja Widdig, a co-senior author of the study and professor at Leipzig University, explains, "Through our in-depth analysis, we found that migrant male orangutans in our study exhibited a higher frequency of peering at food items that are challenging to process or rarely consumed by the local population. This includes foods that were observed being eaten for only a few minutes throughout the entire study duration."
The authors, however, cautioned that the exact number of times adult orangutans need to observe a specific behavior through peering before acquiring mastery remains unknown. Observations suggest that depending on the complexity or novelty of the learned skill, adult orangutans may continue to engage in exploratory behaviors when encountering food items they initially learned about through peering. This behavior may serve purposes such as gaining further insights, reinforcing and memorizing the acquired information, or comparing it with their existing knowledge.
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