In this study, I tested an animal’s use of internal information and external information to make foraging decisions. To test the use of internal information, I investigated whether mandrills use synchrony cues to make foraging decisions. To test the use of external information, I investigated whether mandrills use olfactory cues to make foraging decisions. The study provides evidence that external information in the form of olfaction was used to make foraging choices, but synchrony cues were only used by one individual.  

Use of internal information: synchrony cues

I find that mandrills overall did not make use of internal information in the form of synchrony cues to make foraging decisions. However, the results of only the alpha male indicate that he used synchrony cues. Overall, mandrills would often choose to forage at grape locations first, regardless of what food cue was provided at the entrance to the outside enclosure. Only the alpha male chose to forage at locations that matched the provided cue. These results suggest that as a group, mandrills do not show evidence of using synchrony cues to forage, but that they likely do have the cognitive capabilities to do so. 

These findings are not in line with previous studies which have shown that wild primates use synchrony cues to forage more efficiently. Since mandrills live in a rainforest containing synchronous fruiting trees and mandrills have been reported to have advanced cognitive capabilities, it is unlikely that the use of fruiting synchrony would not be adaptive for mandrills nor is it unlikely that mandrills lack the cognitive capabilities to use synchrony cues. It is more likely that the complex social group mandrills live in limits individual mandrills to display their cognitive capabilities. There could for example be an influence of gazing from the alpha male, which could explain why only the alpha male used synchrony cues in this study. Mandrills have been reported to pay more attention to higher-ranking group members than lower-ranking group members and gazing is used to predict conspecific behaviour in chimpanzees, another social primate species. 

Grapes were a more highly preferred food source than carrots for three individuals, these individuals visited significantly more grape locations than expected. This suggests that these mandrills might not have used information from the food cue to make their foraging decision but instead used an approach wherein they always checked grape locations regardless of the cue, in the hope to find grapes. However, it is intriguing that the alpha male did not utilize this approach and instead relied on information from the synchrony cue to guide its foraging decisions. This could potentially be attributed to individual personality differences. Mandrills who frequently choose to forage more at grape locations might exhibit traits such as lower patience, higher impulsivity, or simply a stronger preference for grapes or a general dislike for carrots. While variations in personality and preferences are inherent within a social group, future studies should place greater emphasis on food preference and try food options that are equally favoured.

In summary, overall mandrills did not seem to use synchrony cues to make foraging decisions but the alpha male did. The alpha male’s foraging decisions are greatly associated with the food cue provided. The other individuals did not indicate the use of synchrony cues, possibly due to the complex social group, effects of rank, or an overall preference for one of the food types. While I must be careful to use the results of one individual to make statements about mandrills in general, the results suggest that mandrills could be able to use synchrony cues to make foraging decisions. This provides a further hint at the ways that animals can use cognition to optimize their foraging. Continued research on the foraging behaviour of other (primate) species will provide new insights into how foraging behaviour evolved and the ecological intelligence hypothesis which states that cognition evolves to meet challenges posed by foraging.

Use of external information: olfaction 

There was a significant effect between a foraging choice being the first foraging choice and that choice being correct, indicating that mandrills use olfaction to make foraging decisions when no other information about where food rewards are located is available. This is one of the first times that the use of olfaction to locate food sources has been assessed in an old-world monkey species. The results of this study add to the growing amount of evidence supporting the importance of the olfactory sense in primates, supporting the idea that the size of the olfactory apparatus cannot be used to reliably predict olfactory abilities. 

Since olfactory cues can be detected from a long distance, the results from this study underline the importance of controlling for the use of olfactory information in foraging studies. Based on previous research, one might not expect olfaction to be important for foraging in old-world monkeys, this study finds that olfaction can be an important sensory modality for foraging, at least when no other available information to predict the location of food is available. It is likely that animals use olfaction along with other available information to make foraging decisions. Wild mandrills could rely on olfactory cues to locate ripe fruit in rainforests where the fruit might be hard to see. This highlights how important it is to learn more about how animals gain knowledge about their surroundings. When olfaction was considered to be of minor significance for primates, past studies on primates may have disregarded this important sense as a factor in shaping foraging decisions. However, this is not just a primate phenomenon, in other animal groups such as birds, knowledge of olfaction is still limited. 

The size of the enclosure somewhat limits the generalizability of these results. While wild mandrills have a whole rainforest to forage in, the mandrills in this study had access to a space of 157 m2. Because of this, it was beyond the scope of this study to investigate the distance from which mandrills could pick up olfactory cues. If one could study mandrills in a more expansive environment, it would be an interesting avenue for future research to investigate from what distance mandrills can start to locate olfactory cues.

In summary, the results of this study indicate that mandrills used olfaction to locate food. As primates were previously thought not to rely on olfaction because of the size of their olfactory bulb, this study supports the idea that the size of the olfactory bulb cannot be used to predict olfactory capabilities in species where olfaction is often overlooked such as primates and birds. This highlights the vital importance of conducting behavioural studies to understand the role of olfaction in behaviour and evolution. 


In conclusion, this study aimed to investigate the use of internal and external information in foraging decisions by mandrills. The results suggest that mandrills did not show a significant overall effect of using synchrony cues as internal information to guide their foraging choices, although the alpha male demonstrated the use of synchrony cues. This could be attributed to the complexity of the social group or individual personality differences. On the other hand, mandrills clearly utilized olfactory cues as external information to locate food sources, indicating the importance of olfaction in their foraging behaviour. The findings challenge the traditional belief that primates have limited olfactory capabilities and shed light on the potential significance of olfaction for wild primate species. Furthermore, the study highlights the need to consider ecological context and individual variations in cognition and preferences when studying foraging behaviour. Overall, this study contributes to our understanding of the importance and evolution of foraging behaviour and supports the ecological intelligence hypothesis, emphasizing the adaptive cognitive abilities of animals in response to their ecological challenges.

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