Periodic Reporting for period 3 - ECOLBEH (The Ecology of Collective Behaviour)
Reporting period: 2022-04-01 to 2023-09-30
To live in a group requires being able to coordinate actions, maintain cohesion, and make decisions. Without these functions, groups would not be able to function, and eventually dissolve or split apart. But how do animals make decisions? Extensive theoretical studies have reached the conclusion that, in most animals, group should resolve through processes akin to voting, where individuals can propose a particular action (a behaviour or a direction of movement) and the group selects the most popular action. However, testing these predictions is challenging, as it requires studying entire groups at once, thus being able to know who all the individuals involved in a decision are, and what each of their preferences are. For this reason, most studies have been conducted in the lab.
The challenge of studying collective decision-making in the wild is substantial. Not only are there methodological hurdles with tracking individuals, but also a whole hosts of factors processes that are absent in captive studies. These include extensive within-group variation among individuals—groups are often composed of both males and females, adults and juveniles; and the environment in which the groups are making decisions changes all of the time. To date, we have very little information about how ecology and group composition impact collective decision-making. The aim of this study is to address this gap.
Understanding how groups make decisions is fundamental to understanding how societies, such as our own, can evolve. Without the ability to resolve between-individual conflict, there is no route to the types of cooperation that we see in humans. Yet, like in animals, our own evolutionary history is rooted in a changing and dynamic environment. The overall goal of this study is to start shedding light on how groups might overcome changes in the environment to be able to continue to function across, and overcome, a wide range of ecological challenges.
The challenge of studying collective decision-making in the wild is substantial. Not only are there methodological hurdles with tracking individuals, but also a whole hosts of factors processes that are absent in captive studies. These include extensive within-group variation among individuals—groups are often composed of both males and females, adults and juveniles; and the environment in which the groups are making decisions changes all of the time. To date, we have very little information about how ecology and group composition impact collective decision-making. The aim of this study is to address this gap.
Understanding how groups make decisions is fundamental to understanding how societies, such as our own, can evolve. Without the ability to resolve between-individual conflict, there is no route to the types of cooperation that we see in humans. Yet, like in animals, our own evolutionary history is rooted in a changing and dynamic environment. The overall goal of this study is to start shedding light on how groups might overcome changes in the environment to be able to continue to function across, and overcome, a wide range of ecological challenges.
The project is primarily based in central Kenya, where a unique species of bird—the vulturine guineafowl (Acryllium vulturinum)—lives. This species forms large groups, which have recently been found to contain multiple reproductive males and females. Further, using GPS tags fitted to individuals in all groups within a population revealed that groups form a multilevel society—they interact regularly and preferentially with individuals from other groups. Based on this foundation, the project set out to investigate the different factors that affect what these groups do. Two key results emerged from this.
First, the size of the group, which ranges from 15 birds to over 60 birds, has a major impact on its movement characteristics. More strikingly, this pattern is non-linear, with intermediately sized groups expressing lower daily travel distances and larger home ranges. These advantageous characteristics suggest that there is an optimal group size for movement—something that has only previously been found in baboons.
Second, the population has experienced a series of droughts since the start of the project, and the response has been striking. As conditions dry, groups start expressing substantially larger home ranges, and often move into completely new areas. As soon as rain starts, they move back into their regular home range, highlighting that these extra-range movements likely correspond to undesired movements outside of a preferred range. This opens up many pressing questions: how do groups make the decision to depart their preferred home range, and how they decide where to move?
The project also investigated what processes might take place within groups when they make decisions. While all individuals can contribute to making a group decision, not all do for each decision. Yet, to date, there had been almost no information about what determined individual contributions. A key finding is that dominance interactions—chases and displacements of one individual by another—are an important predictor of who contributes to a decision. Individuals chased from food then initiate movement to new food places, forcing others to follow. This represents the first field confirmation of an important hypothesis: leadership according to need.
The project has also investigated the factors affecting individual decisions to engage in dominance interactions, finding that these are used very strategically. Individuals only direct high cost interactions (such as chases) to group members that are close in rank to themselves.
Finally, the project has begun investigating some of the energetic of individual and collective movements. Starting with individuals, a major finding was that individuals have particular characteristics when moving large distances—they move straight and fast. These characteristics translate to higher energy efficiency, and the degree to which they express them allows them to almost completely negate the cost of making these large movements.
First, the size of the group, which ranges from 15 birds to over 60 birds, has a major impact on its movement characteristics. More strikingly, this pattern is non-linear, with intermediately sized groups expressing lower daily travel distances and larger home ranges. These advantageous characteristics suggest that there is an optimal group size for movement—something that has only previously been found in baboons.
Second, the population has experienced a series of droughts since the start of the project, and the response has been striking. As conditions dry, groups start expressing substantially larger home ranges, and often move into completely new areas. As soon as rain starts, they move back into their regular home range, highlighting that these extra-range movements likely correspond to undesired movements outside of a preferred range. This opens up many pressing questions: how do groups make the decision to depart their preferred home range, and how they decide where to move?
The project also investigated what processes might take place within groups when they make decisions. While all individuals can contribute to making a group decision, not all do for each decision. Yet, to date, there had been almost no information about what determined individual contributions. A key finding is that dominance interactions—chases and displacements of one individual by another—are an important predictor of who contributes to a decision. Individuals chased from food then initiate movement to new food places, forcing others to follow. This represents the first field confirmation of an important hypothesis: leadership according to need.
The project has also investigated the factors affecting individual decisions to engage in dominance interactions, finding that these are used very strategically. Individuals only direct high cost interactions (such as chases) to group members that are close in rank to themselves.
Finally, the project has begun investigating some of the energetic of individual and collective movements. Starting with individuals, a major finding was that individuals have particular characteristics when moving large distances—they move straight and fast. These characteristics translate to higher energy efficiency, and the degree to which they express them allows them to almost completely negate the cost of making these large movements.
The results of this project are pushing the boundaries of the start of the art. The results outlined above have all provided new dimensions to what are well-established bodies of work.
As the project becomes more established, it is expected that similar results will continue to emerge. Several experiments are underway, and much data has been collected.
As the project becomes more established, it is expected that similar results will continue to emerge. Several experiments are underway, and much data has been collected.