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Vocal and visual mechanisms behind coordinated group movement

Periodic Reporting for period 1 - GROUP MOVEMENT (Vocal and visual mechanisms behind coordinated group movement)

Reporting period: 2018-05-15 to 2020-05-14

Anthropogenic noise (human generated noise) can be heard throughout almost the entire planet, and, aside from other negative effects such as increased stress, this noise can cause large swift declines in bird abundance and species richness. Currently the planet is losing biodiversity at high rates which can have far reaching effects across habitats and processes, including those ecosystem services we rely on. How anthropogenic noise may be causing these declines in biodiversity remains unclear, but anthropogenic noise masking (drowning out) important signals seems to be a key factor. While anthropogenic noise is known to mask important signals like songs and anti-predator warning calls, declines that happen when anthropogenic noise is introduced happen very quickly, even within as little as four days. This suggests that the sounds masked may be more commonly used than sexual or anti-predator signals. One type of call that is used almost all the time by many species are ‘contact calls’ – calls used by groups of individuals to stay together and coordinate group movement through their habitat.
Contact calls are thought to be especially important in habitats with visual barriers like forests as calls travel a lot farther in those types of habitats and can provide information about many different individuals at one time. While vocal coordination of group movement in mammals is somewhat understood, evidence regarding how calls function to maintain group cohesion and coordinate group movement in social bird species is rare. To determine if anthropogenic noise masking contact calls can impact flocking behaviour, the mechanisms behind how these calls are used by individuals to coordinate group movement must be understood. To accomplish this, it is necessary to track not only the position of each individual in the flock, but to determine which individuals are calling from where and when. Combining this with controlled environmental manipulations of both the acoustic and visual environment, we can ask targeted questions about how flocks change their group behaviour and calls to maintain flock cohesion and coordinate movement.
Our objective with this project is to determine how anthropogenic noise may be causing declines in species diversity through masking contact calls. To accomplish this our goal is to answer the following two questions: (1) how to individuals and groups use calls to affect the behaviour of the group and coordinate group movement, and (2) how does the visual and acoustic environment affect the use of vocal coordination of group movement.
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.
This project is the first of its kind, allowing us to track high definition movements and calls of individuals in a group over multiple days in different visual and acoustic environments. This field of research continues to focus on adopting more and more new technologies to allow for finer-scale and more in-depth quantitative methodologies as evidenced by the Summer 2019 Association for the Study of Animal Behaviour Conference: New Frontiers in the Study of Animal Behaviour co-organized by the ER. She has also presented her work at four international conferences as well as during invited lab visits and to the general public, expanding the impact and encouraging further development, collaboration, and use of this novel way of using this technology. This research has developed new methodologies that can be used in future studies in the Imaging Barn, and which have directly led to another 5-year project planned to begin in 2021 examining how nonapeptides influence sociality in flocks of birds.
With the data from these experiments we will be able to include visual, acoustic, and physical impediments into models exploring the mechanisms of group movement that currently exist. Hopefully this will improve the ability for future models of group movement to incorporate different or multiple modes for individuals to maintain contact and bridge the gap between models’ empty space where theoretical movement occurs and ecological realities of cluttered space where group moving species exist. By better understanding both how individuals use calls to coordinate group movement, and how anthropogenic noise affects a group’s ability to do use these calls to maintain cohesion and coordinate, we hope to be able to develop solutions for masking problems arising from anthropogenic noise.
Starling backpack
Visually good and poor setups in the imaging barn