Black howler monkeys create mental maps

Although we’re now all used to looking at Google maps to navigate, in the absence of technology and written maps humans use route based navigation - that is, we go the way we know will get us to where we want to be, even if it’s not the shortest way, and will normally optimise over time. Now, researchers at Oxford Brookes and the University of Texas, Austin have shown that black howler monkeys, who previously have been thought of as having low cognitive abilities, actually navigate through vegetation in search of fruits using mental maps just like us, and are capable of refining their mental maps as they go to optimise their journeys. Eva Higginbotham heard from lead author Miguel de Guinea from Oxford Brookes University...

Miguel - Black Howler monkeys use routes to navigate that resemble the navigation system of humans to a level that we have not seen ever before. So, for a year I was waking up almost every day at four in the morning to follow these guys, we were following them 12 hours a day. We would get to the field, find the tree where they were, sometimes they would howl in the morning. So, howler monkeys howl which means that they engage in very loud vocalisations which you can hear one kilometre away.

Eva - Can you do an impression of one, how do they sound?

Miguel - I think I can do something like that after hearing them so often. It's something like [rather impressive howler monkey impersonation].

Eva - Sounds terrifying!

Miguel - It's kind of terrifying. It resembles a lot like Jaguars. It's pretty...it's very intense when you hear it in the jungle the first time! So, then we will find them in this tree and then we would follow them for the rest of the day. They will be foraging, socialising, having encounters with other groups, and then they would go to their sleeping tree and we would go back home to the research house, and go back again for the sunrise the next morning. So, these monkeys wouldn't travel long distances, but maybe between 300 metres and maybe 800 metres. The thing is that this area's very sloping, it used to be a Mayan city. And on top of this ancient Mayan city, there is a forest. So, there are several changes in elevation that we have to deal with when we are following the monkeys. They navigate in the canopy, but we move on the ground. So, we are all the time going up and down cascades and Mayan temples. So, it's sometimes very daunting, very challenging to get there!

Eva - And what did you find?

Miguel - We found that they do rely on routes very often. It was pretty clear since the beginning that they were using the same routes, but the thing is that they do manage to move very efficiently in the forest. So, when I was analysing the data, I was like, this is not just it, it's not that they are using these routes. So, I was like, there is something going on with the structure of these routes because they navigate in a very straight line despite using previously established routes. Then what I decided to do is to say, okay, so how would a monkey move if it had no cognition? And I simulated movements using an algorithm to just compare. And then what we found is that the observed monkeys develop this set of routes that are highly efficient. So, it allows you to navigate in between any location in the area that is highly relevant to any other location using a very short path. So, they do develop this set of routes that are highly efficient and that's why it seems to me as if they were navigating in a metro. So, they just have the Metro network in their minds and they just use it to navigate.