To answer these questions, we tracked flocks of 12 starlings as they moved through their environment determining where every individual was and where every call came from, allowing us to figure out who called, from where, and when. To do this, we used the Imaging Barn, a special facility at the Max Planck Institute of Animal Behavior, that contains a testing arena with two high definition tracking technology systems. First is the VICON system, a 32 infrared camera tracking system that tracks infrared reflective markers. By making backpacks with unique markers patterns we were able to track the position of all individuals in the flock with sub-millimetre precision at 100 frames per second. Second is the acoustic array designed by Dr. Jens Koblitz. The array is a series of 30 sensitive microphones mounted in the ceiling which we used to record all the calls made by the starlings. Using specialized software, we are able to establish where calls originated in order to determine which birds called when.
We conducted environmental manipulation experiments to address both questions. Each flock experienced four environmental conditions: good (silent, visually open), visually poor (silent, visually restricted), acoustically poor (noisy, visually open), and poor (noisy, visually restricted). To create these different environments, we used infrared-invisible clear and opaque barriers to control how far individuals could see when perching or foraging and playbacks of silence or road noise (which is often encountered in the wild) to control how easy it was to hear one another. By examining movement and calling data from the good condition, we will determine how individuals use calls to coordinate group movement in ideal conditions. By examining movement and calling data from the visually poor and acoustically poor environments we can determine the effects of reducing visual and acoustic contact separately in a controlled setting. Finally, by examining movement and calling data from the poor environment we can determine the effects of anthropogenic noise in many of the habitats birds live in (e.g. forests, etc.).
The sudden unavailability of one tracking method (acoustic tracking for positional location) necessitated a further development and piloting of the visual tracking method (VICON), resulting in a year delay. Therefore, while we have extracted all the data from the experiments, we are still in the process of developing more robust methods to process the raw positional data into 3D individual tracks and fine-tune the acoustic localization methods for starling calls. However, we continue to work towards robust data for analyses examining how individuals coordinate group movement using calls and the effects the visual and acoustic environment has on those calls. We are dedicated to looking at these results as we need to understand how anthropogenic noise affects group movement and contributes to species diversity loss before we can find solutions.
