Collaborative Research: Causes of Variation in Parid Call Complexity

Human language is the most complex communication system known. However, many non-human animal species also have quite complex communication systems, including non-human primates, whales and dolphins, and even many bird species. The key factors driving such complexity, though, remain largely unknown for both human language and for non-human communication systems. Discovering these factors is crucial to understanding the origin and evolution of such complex behavior, including the origin of language in our own ancestors. The proposed research will use observational and experimental methods to test three key factors proposed to explain vocal communication complexity: social complexity and group size, predation risk, and habitat-induced constraints on sound transmission. The investigators will examine these factors in two common North American bird species that possess complex systems of vocal behavior as well as complex social structures: Carolina chickadees and tufted titmice. The researchers will include their results in their teaching and mentor multiple student researchers in current research methods including Big Data management strategies, and collaborting with supercomputing staff through the Extreme Science and Engineering Discovery Environment program associated with the University of Illinois supercomputing facility. Lucas and Freeberg will continue to write about this work for general-audience journals like American Scientist, where they co-authored a 2012 article that has been read by thousands of readers in the U.S. and abroad.

What factors drive the evolution of complex signals? The Social Complexity Hypothesis posits that species or populations forming complex social groups require more complex signaling systems than species or populations that form simpler groups. Although there is increasing evidence to support the Social Complexity Hypothesis, a key limitation is that it is rarely tested against alternative hypotheses. The proposed work tests the Social Complexity Hypothesis against two major alternative hypotheses to explain communicative complexity, using chick-a-dee calls of two avian species of the family Paridae (Carolina chickadees, Poecile carolinensis, and tufted titmice, Baeolophus bicolor): (1) Social Complexity: Individuals in more complex flocks produce calls with greater complexity than individuals in simpler flocks. (2) Habitat Constraints: Individuals in habitats that are more open produce calls with greater complexity than individuals in more closed habitats. (3) Predation Pressure: Individuals in habitats with a greater density or diversity of predators produce calls with greater complexity than individuals facing fewer predators. The hypotheses will be tested with unprecedented resolution through captive flock experiments at the University of Tennessee and University of Florida, data collected on un-manipulated wild flocks, field playback experiments, and observations of flocks before and after scheduled partial forest cuts at the University of Tennessee and Purdue University. The work will increase understanding of the function and mechanisms of complex communicative behavior and provide fundamental information about how complex behavior at the level of the individual emerges from the nature of the social and physical environmental setting in which the individual lives. Parid species are now commonly utilized as a model system for the study of social information use and its fitness consequences in animal communities. This work lays a solid foundation for understanding the nature of parid call complexity and, in turn, the generation of finely tuned information used by many species in fitness-related decision-making in a rapidly changing world. The investigators intend to deposit the data in the University of Tennessee institutional repository, Trace (http://trace.tennessee.edu/), where University of Tennessee Libraries staff will provide appraisal for long-term preservation and stewardship. Trace addresses access, security, preservation, and copyright of deposited research, and ensures that global researchers can find the data, with the assignment of Digital Object Identifiers (DOIs) encouraging proper citation and re-use.