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Only dominant vervet monkeys tackled the hardest food puzzle

Young wild vervet monkey eating a banana in a protected area in Uganda
Research: Behaviour, Ecology

For a vervet monkey (Chlorocebus pygerythrus), getting food can involve more than finding it. If a task takes a long time, another monkey may have the chance to displace the animal doing the work. Here, the time spent working through a food puzzle to get its reward is its handling time. A field experiment with wild vervet monkeys examined how social rank related to foraging choices and how vigilance related to puzzle-solving.

Researchers placed three puzzle boxes in a straight line and offered them at the same time. The boxes became harder to handle and offered greater rewards. Monkeys of different dominance ranks accessed the easier, lower-reward boxes. But only dominant monkeys—those less likely to be displaced—attempted the most difficult box, which also took the longest to handle.

Experience and vigilance

Monkeys became quicker at handling each box as they gained experience with it. The researchers had also predicted a trade-off between vigilance and solving the puzzles: animals that spent more time watching for threats might be expected to work more slowly. Instead, higher vigilance rates were associated with faster puzzle-solving.

The authors suggest that monkeys may be able to scan their surroundings with frequent, brief glances while continuing to work. The finding is an association, but it points to a way vigilance and food handling could occur together rather than requiring a simple choice between the two.

Handling time may affect which food sources monkeys of different ranks attempt to use. A subordinate monkey at greater risk of being displaced may be less likely to start a long task, even when the food is available. The authors suggest that such costs could contribute to rank-related differences in diet.

Sources and image credit

  1. Can’t win, don’t try: handling time costs affect foraging choices and vigilance in wild vervet monkeys (Chlorocebus pygerythrus)Primærkilde; bioRxiv preprint.

Image: Young wild vervet monkey eating a banana in Uganda (2023). Photo: Jameswasswa / Wikimedia Commons, CC BY-SA 4.0. Representative photograph, not from the experiment. · CC BY-SA 4.0 · Source

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