Chimpanzees use least-cost routes to out-of-sight goals

While the ability of naturally ranging animals to recall the location of food resources and use straight-line routes between them has been demonstrated in several studies [1, 2], it is not known whether animals can use knowledge of their landscape to walk least-cost routes [3]. This ability is likely to be particularly important for animals living in highly variable energy landscapes, where movement costs are exacerbated [4, 5]. Here, we used least-cost modelling, which determines the most efficient route assuming full knowledge of the environment, to investigate whether chimpanzees (Pan troglodytes) living in a rugged, montane environment walk least-cost routes to out of sight goals. We compared the ‘costs’ and geometry of observed movements with predicted least-cost routes and local knowledge (agent-based) and straight-line null models. The least-cost model performed better than the local knowledge and straight-line models across all parameters, and linear mixed modelling showed a strong relationship between the cost of observed chimpanzee travel and least-cost routes. Our study provides the first example of the ability to take least-cost routes to out of sight goals by chimpanzees and suggests they have spatial memory of their home range landscape. This ability may be a key trait that has enabled chimpanzees to maintain their energy balance in a low-resource environment. Our findings provide a further example of how the advanced cognitive complexity of hominins may have facilitated their adaptation to a variety of environmental conditions and lead us to hypothesise that landscape complexity may play a role in shaping cognition.

尽管多项研究[1,2]已证实自然活动的动物能够回忆食物资源的位置，并在资源间沿直线行进，但目前尚不明确动物是否可借助对其栖息景观的认知，选择最低成本行进路线[3]。这种能力对于生活在能量波动剧烈、移动成本高昂的复杂能量景观中的动物而言尤为关键[4,5]。本研究采用最小成本建模（least-cost modelling）——该方法基于对环境的完全认知来确定最高效的行进路线——，旨在探究栖息在崎岖山地环境中的黑猩猩（Pan troglodytes）是否会选择最低成本路线前往视野外的目标地点。我们将观测到的移动轨迹的“成本”与几何特征，与预测的最低成本路线、基于智能体（agent-based）的局部认知模型以及直线零模型进行了对比。在所有参数维度上，最小成本模型的表现均优于局部认知模型与直线零模型；线性混合模型分析显示，观测到的黑猩猩移动成本与最低成本路线之间存在显著关联。本研究首次证实黑猩猩具备前往视野外目标的最低成本路线选择能力，表明其拥有对活动领地景观的空间记忆能力。该能力或许是帮助黑猩猩在低资源环境中维持能量平衡的关键性状之一。我们的研究结果进一步佐证了人亚族（hominins）的高级认知复杂性如何助力其适应多样的环境条件，并促使我们提出假说：景观复杂性或许在塑造认知能力的过程中发挥了重要作用。