The fruits of intelligence

Researchers studying the foraging behaviour of monkeys have found a breed intelligent enough to know that warm weather ripens fruit, and to adjust their behaviour accordingly.

The primatologists at the University of St Andrews discovered that the group of mangabeys in Uganda took weather conditions into account when searching for ripe fruit. The monkeys typically revisited trees they remembered held unripe fruit, as long as the weather had been warm and sunny in between. The discovery of this behaviour, by Karline Janmaat, Klaus Zuberbuhler and Richard Byrne, is important since it may have implications for theories of primate cognitive evolution.

PhD researcher Karline Janmaat followed a group of monkeys from dawn until dusk for a period of 210 days in the Kibale Forest, Uganda. Her aim was to investigate whether grey-cheeked mangabeys paid attention to interim weather conditions when searching for ripe figs or unripe figs containing edible insect larvae.

Karline monitored visits of individual monkeys to certain trees and recorded subsequent changes in temperature and solar radiation, both influencing factors in the maturation of fruits. The research group predicted that the monkeys would be more likely to revisit a tree with fruit following several days of warm and sunny weather compared to a cooler and more cloudy period. Karline monitored one group’s foraging among 80 target trees bearing figs, which are a popular source of food amongst mangabeys. Since they do not show obvious visual signs of ripeness and do not fruit during a specific season, monkeys have to squeeze them to assess edibility.

When a monkey came within a 100m circle of a target tree previously visited a few days before, the researcher noted whether or not individuals proceeded to the trunk or simply bypassed the tree. She found that warm weather in between visits significantly affected whether individual monkeys revisited fruit-bearing trees.

The researchers said: “We found that average daily maximum temperature was significantly higher for days preceding revisits compared to bypasses. The probability of a revisit was additionally influenced by solar radiation experienced on the days of re-approach. These effects were only found for trees that carried fruit at the previous visit but not for trees that had been empty.

“Our results are consistent with the idea that monkeys make foraging decisions based on remembering which trees bore fruit as well as a general understanding of the relationship between temperature and ripening of fruit. This use of episodic-like memory (remembering how things were at a specific place when they went there) may have evolved as a selective benefit to anticipate the emergence of new food sources, and is particularly relevant for fruits such as figs which are not predictable by season.”

Since the Kibale Forest has some of the highest primate densities recorded, competition for food is high. The researchers believe that the ability to take weather conditions into account during the search for edible fruits has resulted in more efficient foraging behaviour, thus increasing chances of mangabey survival in a highly competitive rainforest habitat.

The researchers concluded: “Very little work has been conducted to address the idea that primate cognition has evolved to deal with problems of ecological nature, such as efficient foraging for food.

“Our research concluded that these non-human primates were capable of remembering past weather conditions and taking them into account when searching for food, and we believe our findings may have implications for theories of primate cognitive evolution. How exactly the monkeys managed to register the relatively subtle differences in average temperature values, however, remains elusive and a topic for further research.”

The research paper ‘Primates take weather into account when searching for fruits’ by K. R. L. Janmaat, R. W. Byrne and K. Zuberbühler is published in the June 20th edition of Current Biology.

ENDS

NOTE TO EDITORS:

The researchers are available for interview on the following numbers:

Karline Janmaat, 13 June onwards: +31 619944179 (Netherlands, + 1 hour)

19th June onwards: +256-77981085 (Uganda, + 2 hours)

Richard Byrne, 13-20 June: 01334 462051 (St Andrews)

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Ref: Fruits of intelligence 190606.doc

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