Orangutans have a unique dependence on their mothers for an extended period, nursing for at least six years and living with them for several more years. During this time, they learn how to find, choose, and process the diverse range of foods they consume. However, when orangutans leave their mothers and migrate to distant areas with different food availability, how do they decide what to eat and learn how to consume it? A recent study published in Frontiers in Ecology and Evolution suggests that migrant orangutans employ a strategy of observational social learning, observing and imitating the behaviors of local individuals.
The study, conducted by an international team of researchers led by Julia Mörchen, a doctoral student at the Max Planck Institute for Evolutionary Anthropology and the University of Leipzig, examined how migrant orangutan males acquire new ecological knowledge after dispersing to a new area. The researchers found evidence that these migrants learn about food sources and processing techniques from locals through a behavior called “peering.” Peering involves intense observation of a role model for at least five seconds and within a close distance of two meters. The peering orangutans exhibit attentive interest, facing the role model and mimicking their actions with head movements.
Male orangutans typically disperse to new areas after becoming independent, while females tend to remain close to their natal home range. The extent and destinations of male orangutan dispersal are still not entirely known, but genetic data and observations suggest that they undergo long-distance dispersal, potentially covering tens of kilometers and encountering various habitats with different faunal compositions.
The researchers analyzed 30 years of observations collected by trained observers at two research stations: Suaq Balimbing in Southwest Aceh, which studied Sumatran orangutans (Pongo abelii), and Tuanan in Central Kalimantan, which focused on Bornean orangutans (Pongo pygmaeus wurmbii). They examined instances of peering behavior, where males observed neighbors within a 50-meter range. The study included 77 migrant adult males from the Sumatran population and 75 from the Bornean population.
The analysis revealed that peering behavior occurred in 5.2% of the observed associations, with males peering most frequently at local females in the Sumatran population and at adult males in the Bornean population. Migrant males interacted more frequently with the observed food items afterward, putting into practice what they had learned through peering.
Interestingly, the researchers found that migrant males predominantly peered at food items that were challenging to process or rarely consumed by the local population. They even observed migrant males consuming foods that had been recorded as eaten for only a few minutes throughout the entire study period. However, the peering rates decreased after a few months in the new area, suggesting that it takes this amount of time for the migrants to learn about new foods.
While the study provided insights into how migrant orangutan males learn from locals, the researchers noted that the exact number of observations required for adults to master a particular behavior is still unknown. Observations indicate that depending on the complexity or novelty of the learned skill, adults may engage in explorative behaviors with newly learned food items, possibly to gather more information, reinforce their knowledge, or compare it with their existing knowledge.
The ability of migrant orangutans to adapt to novel environments through observational learning likely provided them with a survival advantage over evolutionary time. The researchers suggest that this ability may be ancestral in our hominin lineage, reaching back at least 12 to 14 million years to our last common ancestor with orangutans.