Field Notes: A Life-or-Death Game of Musical Chairs: How Do Baboons Choose Where to Sleep at Night?

Let’s take a little journey back in time. Remember when you walked into a classroom on the first day of school in, say, 8^th grade? If you lucked out and your teacher let you choose where to sit, you had a pretty challenging decision ahead of you, whether you recognized it at the time or not. Maybe you would not want to sit too close to the teacher, because then he or she would notice if you fell asleep during class. But too far from the front of the classroom also is not ideal – the chalkboard might be hard to see from the back of the room. Next to the window could be nice, allowing your mind to wander out of the classroom and into the freedom of the outdoors every time you shift your gaze outside. But what if there is no air conditioning and it gets too hot when the sun shines in? Well, you get the point. There are a lot of physical factors of the classroom that you might consider when choosing where to sit. This, however, is the easy part of the decision. This choice becomes much more complicated (and potentially much more consequential) when your classmates start taking their seats. Suddenly, some of the initial options aren’t available to you anymore. And maybe that seat that didn’t look so great earlier, is a lot more appealing after your best friend sits in the neighboring chair. When you finally make your choice and sit down, this may not be the end of your dilemma, but actually just the beginning of an impromptu game of musical chairs. When the school bully sits down next to you, you might reassess your choice and move to a new spot, in turn causing your best friend to move with you.

Although this typical first day at school may not seem that extraordinary at first glance, navigating this decision-making process is actually incredibly impressive. Ultimately, where you end up will be the result of complex and dynamic social pressures that are overlaid on an already complex and multi-dimensional physical environment. Excited to understand more about how individuals cope with such a complicated decision, I am currently researching how baboons make life-or-death decisions that depend not only on their physical surroundings, but also on the choices of their group-mates.

As the sun goes down on the central Kenyan savanna, baboons seek out a spot in a large yellow fever tree to spend the night. Choosing a good spot is particularly important to getting a good night’s rest and avoiding being eaten by a leopard in the middle of the night.

Baboons offer an ideal system in which to investigate this decision-making process because they actually experience a very similar dilemma to the 8^thgrader on the first day of school. Every night, a baboon will decide with its group-mates (baboons live in stable multi-male, multi-female groups) where on the landscape to take a refuge for the night – either on a cliff face or in a tree. After choosing the general area where they will spend the night, each individual baboon has to then choose where to settle down within the sleep site. Just like in the classroom, the physical characteristics of the sleep site make certain spots better or worse than others. Some spots might be more exposed to rain and wind, while others may provide a less stable sleeping surface. In addition, baboons also face many of the same social pressures as our 8^th grade example. Famous for their complex social networks, baboons have many of the same friend and foe relationships that humans do. However, the consequences of a baboon’s choice of where to sleep at night deviate quite a bit from the classroom analogy. Failing to obtain a preferred sleep spot may lead to poor sleep, which has been linked to a myriad of health issues in both human and non-human primates [1]. A poor choice of where to sleep may also leave a baboon vulnerable to be eaten by a leopard during the night, which is the number one source of mortality for adult baboons [2]. Needless to say, there is substantial pressure favoring a baboon’s ability to successfully navigate this complex physical and social environment when choosing a sleep spot.

Baboons have very rich social relationships that result in complex social networks. These relationships make them a good model system for studying how social dynamics shape behavior and decision-making. Here, baboons assort with their closest family and friends, as they settle down for a little rest and relaxation in the afternoon sun.

But how do we actually study this decision? Naturally, baboons decide where to sleep at night, when it is already dark out and therefore difficult for us to directly observe the choices that they make. Furthermore, understanding the interdependence of group-mates’ sleep spot choices, and thus the social influences on decision-making, requires us to track the choices of all group members simultaneously – a daunting task for only a small handful of observers. So how do we overcome these seemingly insurmountable challenges?

Technology! We work in the field with high-resolution thermal cameras, which enable us to shed light on the half of a baboon’s life that is spent in the dark. We can therefore watch the movements of the baboons throughout the night, allowing us to gain insights into the choices that they are making and the forces driving those choices.

Collecting this nighttime thermal video data takes me to Kenya for about two months of every year, where I observe a group of 50 baboons. Almost every night, this group returns to their favorite sleeping site, a scenic cliff, which forms a natural dam and waterfall overlooking Mt. Kenya (incidentally, my favorite baboon sleeping site as well). I anticipate their return to this site, and every afternoon I set up three high-resolution thermal cameras surrounding the cliff face where the baboons sleep. The thermal cameras film from inside of a housing unit, which protects them from inclement weather and the baboons because apparently baboons really enjoy destroying new and shiny objects in their environment. Each housing unit is a little data collection hub; these housing units protect not only the cameras but also computers which connect each camera to an external hard drive, which stores the over 400 GB of data that results from high-resolution filming for 12 hours. Running a computer and a camera for 12 hours is no small task, energetically speaking, so each housing unit also contains a car battery and inverter which powers the whole system while it runs.

After the cameras, computers, and batteries are in place, I commence the recording and return to the baboon group to make some direct behavioral observations as they make their way towards the sleep site. As darkness approaches, I return to the research center to get some sleep before returning early in the morning to collect the cameras, computers, and batteries to charge them during the day and back up the data they collected the previous night. Traversing some dicey terrain with all of this equipment every day in the African bush has certainly led to some, well, interesting memories. But fiascos aside, this data collection procedure has been very successful, enabling me to collect 15 TB of data on the nocturnal decision-making of baboons over the course of several months.

A baboon poses for the thermal camera on the edge of a precipice where it has chosen to spend the night.

Using these data, we can monitor the sleep spot choices of all baboons simultaneously by leveraging the latest advances in machine-learning. By feeding the videos recorded by the array of thermal cameras surrounding the sleep site into deep neural networks (a type of machine-learning algorithm that mimics a human brain), we can automate the tracking of each baboon’s movements within the sleep site. This produces a readout of the sleep spot choices of all group-mates for the entire night.

A frame from the thermal imagery recording, with bounding boxes representing predictions from a deep neural network object detector trained to detect baboons in our thermal videos. This analytical tool allows us to track the movements of all group members automatically and simultaneously.

With this new thermal technology deployed and the latest machine-learning algorithms at hand, what more do we know about how baboons navigate complex physical and social environments to reach important decisions about where to sleep? Well, with data analysis still underway, you’ll have to wait on the answer to that, but I promise to report back soon!

The team of biologists and computer scientists on the thermal baboon project. This project would not be possible without the generous academic and financial support of my advisor, Meg Crofoot (center, behind sign). This work is also supported by a Richard Coss Wildlife Research Fellowship, the National Science Foundation, and the Max Planck Institute of Animal Behavior.

Carter Loftus is a fourth year Ph.D. Candidate in the Animal Behavior Graduate Group. Carter studies the mechanisms and outcomes of collective decision-making in baboon groups at Mpala Research Centre in Kenya. He enjoys any chance he can get to understand more about how and why social animals interact with their group-mates.

References:

[1] Nunn, C. L., Samson, D. R., & Krystal, A. D. (2016). Shining evolutionary light on human sleep and sleep disorders. Evolution, medicine, and public health, 2016(1), 227-243.

[2] Cheney, Dorothy L., Robert M. Seyfarth, Julia Fischer, J. Beehner, T. Bergman, S. E. Johnson, Dawn M. Kitchen, R. A. Palombit, D. Rendall, and Joan B. Silk. “Factors affecting reproduction and mortality among baboons in the Okavango Delta, Botswana.” International Journal of Primatology 25, no. 2 (2004): 401-428.

[Edited by Maggie Creamer and Josie Hubbard]