Functional vocal communication and social behavior in the California towhee (Pipilo crissalis)

Social animal species must coordinate behavior with conspecifics, and they do so through communication. Communication mechanisms, therefore, shape social interactions and likely evolve via natural selection to maximize individual success within a given social and environmental context. My research described California towhee (Pipilo crissalis) social systems, including their spatial distributions and mating system, and investigated the functional significance of vocal communication behaviors within this context. California towhees are highly sedentary and exhibit life-long social pair bonds. As a result, individuals direct most vocal communication signals toward familiar conspecific individuals, such as neighbors, mates and offspring. One uncommon vocalization type employed by California towhees is a coordinated, unique "squeal" duet performed by social mates. Duetting occurs most often in tropical avian species and a literature review indicated that only 7% of North American passerines perform duets. Duetting was found to be more common among species, like the California towhee, that exhibit year-round territoriality and long-term social monogamy. California towhees are not, however, genetically as well as socially monogamous. 42% of nests in my study population contained extra-pair young. This represents the first demonstration of high levels of extra-pair paternity in a duetting species. Such a high level of extra-pair paternity indicates some degree of conflict between mates, but duets sometimes function cooperatively as well. My results indicated that California Towhees used duets in a variety of contexts, including aggressive extra-pair communication with neighbors or strangers, and intra-pair communication between mates. Experimental playback studies indicated that when pairs duetted in the presence of rivals they used the vocalization to cooperatively defend shared resources. The majority of duets, however, were performed in situations where the duetting partners were both the signal producers and recipients. In these situations California Towhees used duets to coordinate pair-based activities such as raising offspring. Successful offspring production is a critical determinant of evolutionary success, and additional experiments indicated that California towhees are highly attentive to offspring distress signals, and use a location-based decision rule when responding to potential offspring in distress.