Sleeping in Groups

Sleeping in groups offers a variety of advantages such as protection or thermal rewards. Nevertheless, group members have to negotiate the best sleeping spots in alignment with individual social preferences. How do animals resolve these conflicts of interest?

tags sleep, decision-making, baboons

Making good decisions is vital for animals that face life-threatening risks, particularly when it comes to situations when animals are most vulnerable. At night, when group-living animals face predation risk, they still have to consider factors from a complex social environment and multiple physical challenges when choosing an optimal sleeping place. How do animals integrate all these aspects when making critical decisions where to sleep?

To understand the fundamental mechanisms of decision-making of group living animals, including humans, we investigate how wild olive baboons incorporate physical and social parameters in their choice where to sleep.

Similar to humans, olive baboons live in very variable social systems. Multi-male, multi-female groups can range from ten up to one hundred individuals. Within the group, baboons form highly differentiated social relationships with other individuals. They are terrestrial, occupying a wide variety of different habitats, but sleeping in trees or cliffs.

From the nocturnal behavior of baboons, we can learn about the influence of social structures and heterogenous habitats on decision making processes. Further, we gain insight into how predation pressure modulates the social contingencies of decision-making in baboon troops. This helps us begin to understand how these same pressures shaped the evolution of our ancestors’ behavior and social structures, who likely faced similar social and ecological decision-making landscapes to those of extant baboons.

Primates are most vulnerable to predation at night. This nocturnal predation pressure drives baboons to sleep in trees or on cliffs. While predation risk may heavily influence the baboons’ choice of where to sleep at night, additional factors such as shelter from the elements and social dynamics may also have an important influence on this critical decision. By studying how baboons choose where to sleep, we aim to understand how animals navigate complex and multi-dimensional decisions that both influence and are influenced by the decisions of their group-mates.

Where to sleep

At nightfall, a group settles at a suitable sleep site. Upon entering the sleep site, they face a number of factors to consider for making an optimal decision of which sleep spot to choose, as there are potentially more and less coveted spots. This is when the scurrying starts. Where is a stable spot, from which I am not going to fall? Where do I risk being exposed to the elements or even being eaten?

Multiple physical features of the sleep site may be incorporated into the baboons’ choice of where to sleep. We can assign several objective measures to each sleep spot. Factors such as temperature, cover from the elements, stability of the substrate, and accessibility to predators are important aspects when choosing a sleep spot. By using 3D laser scans, we can reconstruct the sleep site including the assigned parameters. At night, we are tracking individuals and assess who is going where, using thermal imagery combined with computer-vision in collaboration with the Department of Collective Behavior.

Whom to sleep with

Additional to physical factors, social parameters seem to influence the baboons’ sleep spot choice. Where are my peers settling? Where is my closest partner? Where do I risk being displaced by a dominant group member? Including all these parameters is a complex decision-making task for an individual within the group. To add some more complexity: the individuals’ decisions are influenced by other individuals’ decisions whose decisions are influenced by yet other individuals… We expect that the social environment maps onto the physical environment, creating a constantly evolving decision-making landscape that updates every time the social environment changes. We aim to assess how social dynamics affect the sleep spot choice. Does a high-ranking individual have priority access to sleep spots? What role play individual characteristics and social dynamics? How do individuals negotiate their preferred sleep spot? To approach this complex social fabric, we have characterized the dominance, affiliative, and kin relationships of group-mates using direct observations supplemented by long-term data of our collaborator Dr. Matsumoto-Oda. We are implementing innovative analytical techniques that draw upon tools from social network analysis to understand how these social dynamics shape decision-making. Subsequently, we will let the baboons tell us which spots they prefer to sleep in. By assessing both physical objective measures and social qualities associated with the preferred sleep spots, we can determine which parameters seem to predominantly drive their decision making.

We can then test how the individuals’ sleep spots influence their sleep quality. By assessing sleep, an important determinant of health in primates, we can evaluate how an individual’s ability to negotiate a preferred sleep spot translates to real consequences. Thus, we are able to test both the mechanisms, as well as the consequences, of decision-making in this system.

Studying these decision-making processes will help us gain a better understanding of how animals deal with the complexities of making decisions in a group when it matters most, and how our earliest ancestors may have faced similar challenges.

Further reading & Cited articles

GPS-identified vulnerabilities of savannah-woodland primates to leopard predation and their implications for early hominins

GPS-identified, low-level nocturnal activity of vervets (Chlorocebus pygerythrus) and olive baboons (Papio anubis) in Laikipia, Kenya

Habitat and social factors shape individual decisions and emergent group structure during baboon collective movement

Blood Biochemical Reference Intervals for Free-Ranging Olive Baboons (Papio anubis) in Kenya

Want to learn more?

To stay together, group-living animals must reach consensus about where to go and what to do. Because individuals differ in their needs and capabilities, group members’ preferences will not always align. Resolving such conflicts of interest is a key challenge to living in stable, socially complex societies. How is influence exerted? How is consensus achieved? more

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