Cognitive maps in the wild: Revealing the use of metric information in black howler monkeys' route navigation

When navigating, wild animals rely on internal representations of the
external world to take movement decisions – called “cognitive maps”. As a
rule, flexible navigation is hypothesized to be supported by sophisticated
spatial skills (i.e., Euclidean cognitive maps); however, constrained
movements along habitual routes is the most commonly reported navigation
strategy. Even though incorporating metric information (i.e., distances
and angles between locations) in route-based cognitive maps would likely
enhance an animal’s navigation efficiency, there has been no evidence of
this strategy reported for non-human animals to date. Here, we examine the
properties of the cognitive map used by a wild population of primates by
testing a series of cognitive hypotheses against spatially-explicit
movement simulations. We collected 3104 hours of ranging and behavioural
data on five groups of black howler monkeys (Alouatta pigra) at Palenque
National Park, Mexico, from September 2016 through August 2017. We
simulated correlated-random walks mimicking the ranging behaviour of the
study subjects and tested for differences between observed and simulated
movement patterns. Our results indicated that black howler monkeys engaged
in constrained movement patterns characterized by a high path recursion
tendency, which limited their capacity to travel in straight lines and
approach feeding trees from multiple directions. In addition, we found
that the structure of observed route networks was more complex and
efficient than simulated route networks, suggesting that black howler
monkeys incorporate metric information into their cognitive map. Our
findings not only expand the use of metric information during route
navigation to non-human animals but also highlight the importance of
considering efficient route-based navigation as a cognitively demanding
mechanism.