Localizing crow vocalizations in social aggregations

The North Creek Wetlands Restoration on the University of Washington Bothell campus is home to a large nocturnal American crow (Corvus brachyrhynchos) roost. Each day from Autumn to Spring, crows form pre- and post-roost aggregations, which consist of tens to hundreds of crows. Crows on these aggregations are often highly vocal, but the functions of their vocalizations are not well understood. Identifying any context-dependent patterns in these vocalizations is critical to fully understand communication in this highly social and intelligent species. Previous studies have shown the presence of human observers near large groups of crows may disrupt natural vocal and non-vocal behavior. In this study, the potential confound of these observer effects are eliminated by recording crow vocalizations using a remotely activated, time-synched microphone array. Simulations are undertaken to study the performance of the Time Difference of Arrival (TDOA) method to localize individual callers. A parametric study is used to analyze the effects of number of receivers, signal frequency and duration, and crow location on the performance of TDOA. In addition to the simulation, different types of recorded crow vocalizations are used to design robust playback experiments to fine-tune our localization technique for use in actual crow aggregations in future.