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.