# Factors Modulating the Occurrence of the Selective-Value Effect in Tufted Capuchin Monkeys (Sapajus spp.)

## TL;DR

This study explores how tufted capuchin monkeys make food choices and finds that their decisions can appear irrational due to factors like food quality and time available for consumption.

## Contribution

The study is the first to investigate the selective-value effect in tufted capuchin monkeys and examine the role of food quality and intertrial interval.

## Key findings

- Capuchins generally preferred the more abundant food option over the single option.
- Some individuals exhibited the selective-value effect, showing no preference between food options.
- Food quality and time available to consume food influenced capuchins' preferences.

## Abstract

Just like human beings, animals often make irrational choices; that is, when making a choice, they do not maximize the amount of food they can obtain. The selective-value effect occurs when individuals show no distinct preference for high-value food when it is coupled with low-value food compared to when it is presented alone. In the present study, we investigated the occurrence of the selective-value effect in twelve tufted capuchin monkeys (Sapajus spp.) by exploring, for the first time in this genus, both the role of food quality and the time available to consume the food. Overall, capuchins preferred the more abundant food option over the single option. However, at the individual level, some capuchins showed the selective-value effect; that is, they did not show a preference for either option. Both food quality and the time available to consume the food modulated capuchins’ preferences. Our findings suggest that apparent irrational decisions might stem from sensory feedback and the need for nutrient intake maximization.

During foraging decisions, animals often make irrational choices. The selective-value effect refers to the lack of preference for an option consisting of one highly preferred item plus one less preferred item compared to a single highly preferred item. A similar bias is the less-is-better effect, in which individuals prefer a single highly preferred item rather than an option that includes both a highly preferred item and a less preferred one. Here, we investigated the occurrence of these decisional biases in twelve tufted capuchin monkeys (Sapajus spp.) by exploring, for the first time in this genus, both the role of the relative value of the highly vs. less preferred food and the length of the intertrial interval. Overall, capuchins made rational choices by preferring the mixed option over the single one. However, on an individual level, some capuchins exhibited the selective-value effect. Mirroring previous findings in apes, both the relative value of the highly vs. less preferred food and the length of the intertrial interval modulated capuchins’ preference for the mixed option. This study provides further insight into the factors influencing violations of rationality in primate food choices, suggesting that these decisions might reflect cognitive adaptations for optimizing sensory feedback and nutrient intake rather than being irrational.