Mechanisms and adaptive consequences of group decision-making in a communally nesting bird

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Solving collective problems is one of the central challenges of group living. When individuals prefer different outcomes, how do societies agree on one choice for everyone? Human groups have developed a variety of methods, from despotism to democratic voting. Collective decision-making in animal groups is less well understood, although examples are ubiquitous: a honeybee colony picks a new location for the hive; a monkey troop invades a neighboring territory; a flock of birds changes its roost site. Theoretical models have been developed to predict the conditions under which such decisions should be shared, and how the structure and stability of the social group might influence the speed and accuracy of these decisions. However, experimental studies on wild animals are rare, leaving gaps between theoretical predictions and empirical evidence. This project explores these gaps in a tropical bird, the greater ani. Anis nest in social groups composed of several pairs, which build a single nest in which all of the females lay their eggs. The choice of where to build the nest is a crucial decision, since its location determines its exposure to predators. The project combines field experiments, behavioral observations, and tracking techniques to test how groups arrive at shared decisions - and, crucially, which opinions prevail when group members disagree. This project will provide research experiences to students and a postdoctoral researcher, training to Panamanian researchers through a series of public workshops, and outreach to the public through a partnership with the Smithsonian Tropical Research Institute. This project explores three major questions about collective decision-making that have arisen from recent theoretical work. First, do shared decisions become less democratic as delays in decision-making grow more costly? Second, can a well-informed minority exert disproportionate influence over group decisions? Third, how does social network structure affect the equality, speed, and accuracy of collective decisions? The research plan leverages a long-term (10-year) data set on greater anis in Panama, which live in groups containing multiple unrelated breeding pairs. Some groups are remarkably stable, consisting of the same members for over a decade; whereas others consist of a mix of experienced individuals and newcomers. Anis show close affiliative relationships with other group members who are not their mates, and prior research has found that the duration of these relationships affects coordinated behaviors. In this project, conflicts of preference between group members will be created by manipulating nest-site quality and the information available to different individuals. This will enable hypothesis testing of how group members arrive at collective decisions when their opinions conflict, how individuals communicate preferences, and whether the presence of well-informed individuals changes the outcome of collective decisions. Knowledge of individual life histories and natural variation in group stability, combined with RFID tracking data on interactions between group members, will reveal how social network structure affects the process and outcome of collective decision-making.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.