Migrant orangutans learn what foods are good to eat by observing local people

Orangutans depend on their mothers longer than any other non-human animal, nursing until they are at least six years old and living with them for up to three more years, learning how to find, select and process a wide variety of foods. they eat. But how do orangutans who have abandoned their mothers and now live far from their birth areas, where the food available may vary widely, decide what to eat and figure out how to eat it? Now, an international team of authors has shown that in such cases, migrants follow the ‘observe, and do as the locals’ rule. The results are published in Frontiers in Ecology and Evolution.

“Here we show evidence that male migrant orangutans use observational social learning to learn new ecological knowledge from local individuals after dispersing to new areas,” said Julia Mörchen, doctoral student at the Max Planck Institute for Evolutionary Anthropology and the University of Leipzig. in Germany, and the lead author of the study. “Our results show that migratory males not only learn where to find food and what to eat from the local population, but also continue to learn how to prepare this new diet.”

Mörchen and colleagues demonstrated that male migrants learn this information through a behavior called ‘peeking’: observing intensely for at least five seconds and from two meters away on a role model. Typically, peeking orangutans face role models and show signs of following their actions with head movements, indicating attentive interest.

Male orangutans migrate to other areas after becoming independent, while females tend to stay near their birth areas.

“What we don’t know yet is how far the male orangutans have spread, or where they have spread. But it’s possible to make educated guesses: genetic data and observations of orangutans crossing physical barriers such as rivers and mountains suggest long-distance distribution, likely over tens of kilometers,” says Mörchen.

“This implies that during migration, males likely encounter multiple habitat types and thus experience different faunal compositions, especially when crossing habitats at different altitudes. Over evolutionary time, being able to adapt quickly to a new environment by taking in important information from the locals, likely gave individuals a survival advantage. As a result, this ability is likely an ancestor in our hominin lineage, reaching at least between 12 and 14 million years from the last common ancestor with the orangutan.”

The authors analyzed 30 years of observations, collected by 157 trained observers, of 77 very sociable migrant adult male Sumatran orangutans. I put abelii at the Suaq Balimbing research station in Southwest Aceh, and 75 adult male migrants from the less sociable Bornean orangutans Pongo pygmaeus wurmbii at Tuanan station in Central Kalimantan. They focused on each observation of peeking behavior during 4,009 occasions when this male was within 50 meters of one or more neighbours, which could be adult females, juveniles, or adult males.

Peeking by males was observed 534 times, occurring in 207 (5.2%) of these associations. In Suaq Balimbing, males stalk local females most often followed by local juveniles, and the least number of adult males. In the less sociable Tuanan population, the reverse occurred: males stalked adult males most often followed by immature orangutans, and least among mature females. Migrant men in Tuanan may lack opportunities to peek at local women, as women are known to avoid prolonged association with those in this population.

Migrant men then interacted more with the food peeked after, practicing what they learned through peeking.

“Our detailed analysis further revealed that the male orangutan migrants in our study most frequently observed foods that were difficult to process, or that were rarely eaten by local people: including foods that were recorded as having been eaten only for a few years. minutes, throughout the study time,” said Dr Anja Widdig, a professor at the University of Leipzig and the study’s senior co-author.

“Interestingly, the peeping rate of migrant males decreased after several months in a new area, implying that this is the time it took for them to learn about a new food,” added Dr Caroline Schuppli, group leader at the Max Planck Institute. Animal Behavior at Konstanz, and senior co-author.

The authors caution that it is still unknown how many times an adult orangutan needs to observe a certain behavior in order to learn to master it. Observations suggest that depending on the complexity or novelty of the skill being learned, adults may still use exploratory behavior on certain foods they first learned through peeking – perhaps to find out more details, reinforce and remember new information, or to compare recent information. . with prior knowledge.