Higher Order Thinking: Orangutans Compare Apples to Bananas, Evaluate Tool Use

Apes are so intelligent that they weigh their options.  This is the conclusion of a new animal cognition study that tested orangutans’ ability to compare, contrast and make decisions based on the best option.

Study overview

Scientists studied tool related decision-making in a non-human primate species, orangutans. They found that the apes carefully weighed their options:  (1) eat an immediately available food reward or (2) wait and use a tool to obtain a better reward instead. To do so the apes considered the details such as (a) differences in quality between the two food rewards, and (b) the functionality of the available tools in order to obtain a high quality food reward, even when multidimensional task components had to be assessed simultaneously…

In their natural habitat, the evergreen rainforests of Borneo and Sumatra, orangutans have to consider several factors simultaneously, such as the predictability to find ripe fruits, the distance and reachability of food as well as the available tools to open extractable food sources. So far it was unknown how orangutans adapt their decisions when the use of a tool is involved and how many factors they can process at the same time in order to make profitable decisions.

Researchers from the University of Vienna, the University of Veterinary Medicine Vienna and the University of St Andrews investigated for the first time how orangutans adapt their decisions when the use of a tool is involved and how many factors they can process at the same time in order to make profitable decisions at the Wolfgang Koehler Primate Research Center in Leipzig.


The researchers used two different types of food items: Banana-pellets, which are the orangutans’ most favourite food type, and apple pieces which they like but disregard if banana-pellets are available. They could extract these items from two different apparatuses: an apparatus required probing with a stick tool to obtain the food item while the other required dropping a ball inside it. Each apparatus could only be operated with the respective tool. During testing, orangutans were confronted with either one or two baited apparatus/es and a choice between two items (usually a food item and a tool). Once the apes had picked one item the other was immediately removed.


Orangutans flexibly adapted their decisions to different conditions:

“If the apple piece (likeable food) or the banana-pellet (favourite food) was out of immediate reach inside the apparatus and the choice was between an immediate banana-pellet and a tool, they chose the food over the tool, even when the tool was functional for the respective apparatus.

However, when the orangutans could choose between the apple-piece and a tool they chose the tool but only if it worked for the available apparatus: For example when the stick and the likeable food was available but the apes faced the ball-apparatus baited with the favourite banana-pellet, they chose the apple-piece over the non-functional tool.

However when the stick-apparatus with the banana-pellet inside was available they chose the stick-tool over the immediate apple-piece.

In a final task, that required the orangutans to simultaneously focus on the two apparatuses, one baited with the banana-pellet and the other with the apple and the orangutans had to choose between the two tools they were still able to make profitable decisions by choosing the tool that enabled them to operate the apparatus with the favorite food.”

-Dr. Isabelle Laumer, researcher


“Our study shows that orangutans can simultaneously consider multi-dimensional task components in order to maximize their gains and it is very likely that we haven´t even reached the full extent of their information processing capabilities.”

-Dr. Josep Call, researcher, University of St Andrews




A Special Message to the Public

“According to a 2007 survey by the United Nations Environment Program (UNEP) orangutans will be extinct in the wild within two decades if current deforestation trends continue. Habitat loss due to extensive palm-oil production is the major threat.

Unfortunately palm oil is still the most widely used vegetable oil in the world. As long as there is a demand for palm oil and we keep buying products that contain palm oil, more and more of the rain-forest will be destroyed. Each of us can positively impact the survival of these extraordinary animals by making purchase decisions that may appear small, but that can collectively make a huge impact on our planet.”

—Dr. Isabelle Laumer , researcher



Journal reference: Isabelle B. Laumer, Alice M. I. Auersperg, Thomas Bugnyar, Josep Call. Orangutans (Pongo abelii) make flexible decisions relative to reward quality and tool functionality in a multi-dimensional tool-use task. PLOS ONE, 2019; 14 (2): e0211031 DOI: 10.1371/journal.pone.0211031


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