After humans, orangutans are the animals in which maternal dependence lasts the longest: it takes them up to 15 years to be weaned and to “give up” their mother to start a life of their own. During this long educational period, orangutans acquire a series of skills that will be useful for them to survive: the most important of these is their menu.
These primates in fact have a “mental catalogue” of around 250 edible plants and animals, which helps them to orient themselves in the food variety of the forests in which they live. A study published in Nature Human Behavior analyzes precisely this ability of orangutans to remember hundreds of foods, and the title already explains everything you need to know: Culture is critical in the development of orangutan diets.
At cooking school. To be more correct, the study investigated an essential aspect of the orangutan diet: is an individual able, on his own, to learn all the foods he needs, or is the species’ menu broader than the individual’s capabilities? To find out, the team had to draw on data from a population of Sumatran orangutans living in the swampy forests of Suaq Balimbing, Indonesia.
We are talking about 12 years of daily and timely observations, which document the behavior of orangutans (almost) minute by minute: enough to understand how they build their food catalogue.
Simulation. However, the team also wanted to understand what happens when you “cut off” a young orangutan from any social interaction, and force him to learn on his own what is edible and what is toxic. And since such cruelty certainly cannot be inflicted on wild orangutans, the scientists focused on a simulation, which was fed large quantities of behavioral data relating to the primates and their lives from birth to 15 years.
The simulated orangutans were gradually stripped of three essential social skills for learning about food: direct observation of another orangutan eating, proximity to other orangutans who are gathering food (which can lead to imitation), and being accompanied by other orangutans in food-rich areas.
The importance of imitation. The simulation results confirmed the data obtained from field observations: the virtual orangutans who had access to all three behaviors built an edible menu of around 220 different foods, a figure comparable to the 250 that primates learn in the wild.
By suppressing one or more of these social behaviors, the orangutans in the simulation instead built a smaller catalog.
In short, the diet of orangutans is first of all a cultural question: the younger specimens learn from the older ones, observing and interacting with them, just as the elderly themselves had done with their predecessors in their time. Without this transmission of information, orangutans would not be able to remember so many different foods, and their food options in the wild would be very limited.
