This award supports Professor Christopher Clark of Cornell University and a graduate student to collaborate with two groups of European biologists in a study of songbird communication. Professor Clark has developed a passive acoustic system for locating vocalizing animals using an array of microphones. The system computes the locations of individual birds which are vocalizing anywhere within 200 meters of the center of the array. This technique allows him to simultaneously follow the movements and acoustic behaviors of many different birds within a community and study the details of their vocal interactions. He will apply this system to two well marked and studied populations of European birds through field work in England with Dr. Peter McGregor of the University of Nottingham and in Denmark with Dr. Torben Dabelsteen from the University of Copenhagen. These collaborators have marked populations of blackbirds and other species, and have pioneered interactive playback systems that are biologically meaningful. Bird song and singing behavior among territorial birds are very complex and poorly understood phenomena. This research plan introduces innovative techniques that will help surmount technical problems associated with studying communication networks. The results should be significant new information about how animals communicate with their vocalizations.