A window into the lives of wild baboons

Summary

In the Department for the Ecology of Animal Societies at the Max Planck Institute of Animal Behavior & the University of Konstanz, Prof. Meg Crofoot leads a research team that is using e-obs technology to gain new insights into the social behavior of wild animals.

ow does a baboon group stay together all day while moving and foraging? How do a baboon’s social relationships shape the decisions that he or she makes about where and when to move, where to sleep, and who to hang out with? Using high-resolution tracking technologies provided by e-obs, we have an unprecedented window into the lives of baboons, providing us with exciting new insight into how their societies emerge and function.

uch of our work focuses on olive baboons (Papio anubis) living in savannah and dry woodland habitat in Central Kenya. Baboons live in large, multi-male multi-female, social groups that travel, feed, and sleep together. By simultaneously fitting many individuals in the same social group with collars set to record high-resolution GPS and ACC data, we can see where, when, and how each individual baboon moves in relation to its group members, and better understand how a baboon group negotiates conflicts of interest to reach a consensus about where to go and what to do.

aboons have complex social lives. Just like people, baboons have strong relationships with their group-mates: some are family, some are friends, some are rivals. In the field, it can be difficult for a human observer to fully document the many social interactions occurring between all group members, or to quantify social patterns that might only be clear from a birds-eye-view. By simultaneously and continuously tracking each group member’s movement, however, we can quantify their social interactions, and characterize their social relationships. We can document who spends time with whom, who follows whom, and who avoids whom, and thus gain valuable insight into baboons’ social lives. In a highly despotic and differentiated animal society such as baboons’, these social relationships have fundamental consequences for individuals’ survival and reproduction. Understanding how these social relationships shape individual- and group-level behavior is a fundamental aspect of our research.

A baboon social affiliation network. Nodes represent individual baboons (colored by their age-sex class), and the width of the lines connecting the notes represent the rate of sitting in close proximity. Thicker lines indicate more affiliative relationships. Source: R. Harel, unpublished data

Because baboon body size is so variable – from the largest males to the smallest independent juveniles – locomotor capacity varies tremendously within a single group. These differences have important implications for how groups travel and mean that maintaining cohesion poses something of a challenge. Generally, studies of animal locomotor biomechanics take place in laboratory settings. Now, however, we can extract fine-scale information about individual biomechanics from tri-axial accelerometer data.  Baboon’s footfalls leave distinctive traces in the data as they walk, allowing us to determine stride frequency, even in the wild. We can see which individuals adjust their stride the most, slowing down or speeding up, in order to stay with the group, and how an individual’s position within the group – whether they’re out in front or behind in the back – affects how they modulate their stride. From the accelerometry data, we can also calculate dynamic body acceleration, which is a well-established proxy for energetic expenditure. This is a simple, relatively non-invasive way of seeing, under natural conditions, which individuals pay the most to keep up with their group (spoiler alert: it’s the small ones!). 

Tri-axial accelerometer measures extracted from a baboon’s collar, plotted over time. The blue line represents the Z-axis (dorsal-ventral) acceleration. Peaks in the blue line indicate footfalls. Source: R. Harelunpublished data

We can then combine these fine-scale observations of the social relationships and locomotor biomechanics of baboons to investigate aspects of baboon life that have, until now, been a mystery. For instance, we are using GPS and ACC data, in combination with thermal imaging  video cameras, to better understand what goes on in baboon troops when it is too dark to see. Baboons are especially vulnerable to predation at night, and therefore baboon groups sleep in relatively protected sites, such as on cliff faces or up in the terminal branches of large trees. We don’t know, however, where each individual chooses to sleep within the sleep site, and how individuals make this decision. Do baboons choose to sleep amongst their friends? Do baboons compete for positions that are far away from the paths through which a predator might enter the sleep site (ex. the trunk of the sleeping tree)? Does an individual baboon’s sleeping spot, or the group-mates near whom it sleeps, affect the quality of its sleep? Despite the importance of sleep for individual fitness, we know very little about what actually goes on among wild animals at night. With the help of eObs technology, we can use baboons as a model system to better understand how individuals’ complex social relationships influence their navigation of heterogeneous physical environments, and how these decisions impact sleep.

A close-up thermal image of a baboon, and (right) a thermal image of a baboon group in its sleep site (the bright yellow dots are baboons’ faces). Photo credit: C. Loftus, unpublished data

The next generation of tags that e-obs is developing will include IMUs (inertial movement units) which have 9-axis of inertial measurements. With these tags on our baboon collars, we’ll gain an even more accurate and detailed representation of baboon behavior, including insights into such things as individuals’ body posture. From this, we can infer the direction in which a baboon is looking and thus we have the opportunity to answer deeper questions about individuals’ attention and decision making. Where is a baboon looking and which of its group members can it see? How does this affect where a baboon chooses to move? How does a baboon’s dominance rank, or position within the group, affect its feeding rate or how vigilant it is about checking its surroundings for potential predators? With these new tags, we’ll be able to take a baboon’s-eye-view of the world, and further expand our window into the complex social tapestry of their lives.

Our baboon research team in Kenya. Photo credit: T. Berger-Wolf

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