Disputes often arise among animals competing for limited resources. In such circumstances, animals may avoid direct combat through use of stereotyped communication signals, such as visual or vocal displays. Prior studies by the co-PI on vocal signaling in a songbird, the black-throated blue warbler, showed that two vocal display features are particularly "honest" signals of threat, in terms of forecasting future aggression. Specifically, the production of extremely quiet songs ("soft" songs) and a certain song category ("type II" songs) both reliably predict whether a bird will subsequently attack a model opponent. The first part of proposed research will test whether these two signal features convey differing levels of threat, and if and how birds may escalate aggressive interactions by modulating these two song features either alone or in sequence. Towards this end, a field experiment will simulate interactive song contests that escalate in intensity. Birds that respond with type II songs during low levels of escalation are predicted to give soft songs during higher stages of escalation, with each higher stage becoming a more reliable predictor of eventual attack. This experiment will indicate whether animal disputes follow a hierarchical "ladder" of escalation, as has been predicted in recent theoretical work. The second part of proposed research asks if and how animals benefit through their use of threat displays. Natural variation among males in threat display use will be documented, and "winners" and "losers" of vocal interactions coded based on who backs down first. Genetic paternity analysis will provide estimates of correlations between threat displays and reproductive success. Males that more frequently use threat displays and "win" more interactions against opponents are predicted to be more successful at siring offspring. This project will provide field research experience for undergraduates, and will be showcased in outreach activities to elementary school students.
This research examined the processes by which animals negotiate conflicts through the use of communication signals, and how the outcomes of that negotiation affects animals' future reproductive success. First, we examined whether animals communicate ‘honest’ information during disputes despite strong incentives for bluffing. Specifically, we explored the idea that during aggressive interactions that progressively escalate in intensity, animals use sequences of communication signals that convey increasing levels of threat, with each subsequent signal being more honest about an impending physical attack. We used a novel experimental approach that simulated gradually escalating interactions in a songbird species, the black-throated blue warbler. We found that birds which sang certain types of songs early in interactions were more likely to sing quiet versions of songs (soft songs) later in interactions. Moreoever, birds that sang soft songs were more likely to attack a model opponent. While the idea that animals escalate interactions by using increasingly threatening signals has been received attention in recent years, our study provided some of the first experimental supporting evidence for this idea. Second, we investigated whether the outcomes of conflicts affect the future success of participants. We specifically focused on paternity success of males, a key determinant of male reproductive success. We observed natural interactions among competing male black-throated blue warblers in the field and characterized the outcomes. We also sampled genetic material from all young produced in the study area in order to conduct a genetic paternity analysis. Our preliminary results suggest that the outcomes of disputes between males is related to their mating success, with males that emerge as "winners" in interactions siring more offspring. This is one of the first studies that links communication during conflicts with reproductive success in the wild. This research provided many training opportunities for students. First, funding allowed the co-PI to expand the scope of his doctoral dissertation, and to spend part of a semester at another university in order to learn and gain experience in genetic lab techniques. This experience has diversified his background as a scientist and helped him build interdisciplinary collaborations at another university. Second, this research involved the participation of eight undergraduate students who assisted in field work, lab work, and/or data processing and analysis. These experiences enabled students to learn and build many skills involved in field and lab biology, and provided training and inspiration to pursue future careers in science. This research has also been disseminated to a wide audience. Results have been published in Proceedings of the Royal Society, a high impact and widely read scientific journal, and additional manuscripts are currently being prepared for future publication. In addition, this research has been presented publicly at several venues including the University of Brasilia, Brazil, the North American Ornithological Conference, the University of Massachusetts Life Sciences Graduate Research Symposium, and the Animal Behavior Society annual conference. In addition, the co-PI has also discussed this research in a guest talk for a scientific methods course at Hampshire College, to help illustrate the process of science and developing research ideas.
