Research Article: Orangutans (Pongo abelii) make flexible decisions relative to reward quality and tool functionality in a multi-dimensional tool-use task

Date Published: February 13, 2019

Publisher: Public Library of Science

Author(s): Isabelle B. Laumer, Alice M. I. Auersperg, Thomas Bugnyar, Josep Call, Darrell A. Worthy.


Making economic decisions in a natural foraging situation that involves the use of tools may require an animal to consider more levels of relational complexity than merely deciding between an immediate and a delayed food option. We used the same method previously used with Goffin´s cockatoos to investigate the orangutans’ flexibility for making the most profitable decisions when confronted with five different settings that included one or two different apparatuses, two different tools and two food items (one more preferred than the other). We found that orangutans made profitable decisions relative to reward quality, when the task required the subjects to select a tool over an immediately accessible food reward. Furthermore, most subjects were sensitive to work-effort when the immediate and the delayed option (directly accessible by using a tool) led to the same outcome. Most subjects continued to make profitable decisions that required taking into account the tool functionality. In a final multidimensional task design in which subjects had to simultaneously focus on two apparatuses, two reward qualities and two different tools, the orangutans chose the functional tool to access the high quality reward.

Partial Text

Making rational economic decisions in natural foraging situations requires balancing costs (such as time spent to travel to a feeding patch) and benefits (such as gaining food of higher quality). Moreover, such decisions often require individuals to consider several factors simultaneously including the predictability of finding a more valued/ ripe food source, the reachability of the food source as well as the presence of the proper means /tools to open up an extractable food.

Orangutans maximized the quality of their food intake by flexibly choosing between a food item and a tool depending on the conditions. In particular, they chose a tool over an immediately accessible food item to obtain a more preferred food item (using the tool) but they chose the immediate food item over the tool if the apparatus contained the food item of a lower quality (Quality allocation test). Additionally, the majority of subjects showed work-effort sensitivity by choosing the immediate food option over the tool if the food inside the apparatus was of the same quality (Motivation test). Four of the six orangutans made profitable decisions when the task required the subjects to simultaneously focus on the functionality of the tool as well as on the reward quality (Tool functionality test). Furthermore, when subjects faced both apparatuses (each baited with food items that differed in quality) and both tools (Tool selection quality allocation test), all orangutans chose the functional tool to operate the apparatus containing the higher quality food.




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