Transitions from solitary lifestyles to group living, and from loose aggregations into highly integrated, socially differentiated social groups have occurred a number of times over evolutionary history. Living in stable social groups allows animals to reap the benefits of collective action by collaborating with their group-mates to achieve greater reproductive success than would be possible as a solitary individual. 

Group-living also creates a unique and complicated set of behavioral challenges, especially when conflict arises between individual and group interests. In my research, I use white-faced capuchin monkeys (Cebus capucinus) as a model for exploring how group-living individuals balance their own needs against those of their social group, and how cooperative group actions shape patterns of individual behavior and fitness. 

For my post-doctoral research, I am investigating when, why, and how capuchin monkeys cooperate with group-mates to defend shared resources.

For a group win such interactions, a large percentage of its members must participate. However, competition is potentially costly (individuals that fight risk serious injury) and, like many other cooperative behaviors, poses a collective action problem: cheaters who do not participate are better off than cooperators, since they gain all the benefits without paying any of the costs. In capuchins, participation in intergroup competition tends to be highly variable.  

My current research explores why individuals cooperate in some situations, but not in others, by experimentally manipulating the location and social context of interactions among capuchin social groups using recordings of capuchin vocalizations.   

Past Research:

Intergroup conflict and the home field advantage

My dissertation research explored how group characteristics shape competitive ability and influence individual behavior and foraging success in capuchins. Capuchin groups compete over access to resources, such as food and mates, which are critical for survival and reproduction (Crofoot, 2007).

Despite the potential importance of intergroup competition for understanding patterns of population growth and demography in social species (Robinson, 1988; Packer et al., 2005), the determinants of victory and its impact on the reproductive success of group members remains poorly understood. This is largely because intergroup interactions are relatively infrequent, making it difficult to obtain a sufficient sample size to distinguish between competing hypotheses.

I overcame this challenge by using a novel technology, an Automated Radio Telemetry System (ARTS), to simultaneously monitor the movements of multiple capuchin groups. This method enabled me to detect many more intergroup interactions than traditional techniques would have yielded in an equivalent period.

Field station on Barro Colorado Island, Panama

One day of ARTS data from 12 capuchins in 6 groups

I found that the odds of winning increased with relative group size, but that the effect was not uniform across space.Small groups were able to defeat much larger groups in the center of their home range, but their competitive ability decreased sharply as they moved towards the periphery of their range. In contrast, large groups were highly likely to win interactions regardless location. 

What is the cost of belonging to a small, subordinate group? Using ARTS data, I demonstrated that intergroup relationships decrease the foraging efficiency of low ranking groups by increasing their travel costs and restricting their space use (Crofoot, 2008). These disadvantages did not have an obvious impact on diet quality, but behavioral data suggested that low ranking groups had to work harder (i.e. increase their foraging effort) to maintain their high diet quality. These results indicate a clear cost to subordinancy, and suggest that the competitive advantage offered by large group size may translate into a foraging, and thus fitness advantage for the individuals living in large social groups.