Chacma baboons (Papio ursinus) intentionally overturn rocks to feed on the invertebrates beneath. However, baboons do not move all the rocks they encounter, with this presumably reflecting cost–benefit (or effort–reward) trade‐offs in their foraging behavior. We ask, how do “clever baboons” choose rock sizes and shapes and move these rocks? Using optimal foraging theory, we predicted that baboons would prefer to move medium‐sized rocks, a trade‐off between moving larger rocks that might require more effort to move, and smaller rocks that likely do not provide enough prey (the reward) to make the effort worthwhile. We also expected baboons to prefer rounded rocks as these will require less energy to move by rolling (rather than being flipped as for flat rocks) and that the effort of rock movement might be offset by moving rocks along the shortest axis. We show that baboons have clear preferences for specific rock sizes (medium‐sized) and shapes (angular and flat when these were medium‐sized), and the way in which rocks are moved (along the shortest axis). Prey occurred infrequently under rocks. The low predictability of prey beneath rocks suggests that such prey, when encountered, is of considerable value to baboons for them to expend the search effort, and also explains the extensive nature of rock movement by baboons in the landscape. Our study provides a novel application of the optimal foraging theory concept and has important implications for understanding and predicting how animals choose to move rocks.

中文翻译：

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聪明的狒狒应该如何选择和移动岩石？

Chacma狒狒（Papio ursinus）故意翻倒岩石，以其下方的无脊椎动物为食。但是，狒狒并不会移动遇到的所有岩石，这大概反映了觅食行为的成本－收益（或努力－回报）折衷。我们问，“聪明的狒狒”如何选择岩石的大小和形状并移动这些岩石？使用最佳觅食理论，我们预测狒狒会喜欢移动中型岩石，在移动可能需要更多努力才能移动的较大岩石与可能无法提供足够猎物（奖励）的较小岩石之间进行权衡值得的努力。我们还期望狒狒会喜欢圆形的岩石，因为它们通过滚动运动所需的能量更少（而不是像平坦的岩石那样被翻转），并且岩石移动的努力可能会被沿最短轴移动的岩石所抵消。我们显示，狒狒对特定的岩石大小（中型）和形状（中等大小的角形和扁平形）以及岩石的移动方式（沿最短的轴）具有明显的偏好。猎物很少发生在岩石下。岩石下猎物的可预测性低表明，这种猎物遇到时，对于狒狒来说很有价值，因为它们可以花费更多的精力进行搜索，并且还解释了狒狒在景观中运动的广泛性。我们的研究为最佳觅食理论的概念提供了新颖的应用，对理解和预测动物如何选择移动岩石具有重要意义。猎物很少发生在岩石下。岩石下猎物的可预测性低表明，这种猎物遇到时，对于狒狒来说很有价值，因为它们可以花费更多的精力进行搜索，并且还解释了狒狒在景观中运动的广泛性。我们的研究为最佳觅食理论的概念提供了新颖的应用，对理解和预测动物如何选择移动岩石具有重要意义。猎物很少发生在岩石下。岩石下猎物的可预测性低表明，这种猎物遇到时，对于狒狒来说很有价值，因为它们可以花费更多的精力进行搜索，并且还解释了狒狒在景观中运动的广泛性。我们的研究为最佳觅食理论的概念提供了新颖的应用，对理解和预测动物如何选择移动岩石具有重要意义。