Date of this Version
Goller, M. (2020). Functions of vocal mimicry in the complex song of the European starling, Sturnus vulgaris. [Doctoral thesis, University of Nebraska-Lincoln]. Digital Commons.
Vocal learning is an ability that has only evolved in a handful of taxa. Songbirds learn their songs, and some species have flexible learning in which they not only incorporate species-specific sounds, but heterospecific and/or environmental sounds as well. The functions of vocal mimicry are still unknown for many species and studying mimicry can teach us about the variation within the song learning process. In this thesis, I focused on five hypotheses on how mimicry could function in sexual selection. The repertoire size hypothesis suggests that selection for larger repertoire sizes allows mimicry to occur because imitation can increase repertoire size. The permissive learning hypothesis states that heightened song complexity requires a relaxed song template, which may allow passive use of mimicry. The learning and performance hypothesis suggests that learning ability and song or performance quality are honest signals of a singer’s quality and that listeners may focus on mimicry to assess individuals. The fourth and fifth hypotheses, which have received very little attention, are the structural function and acoustic function hypotheses, which suggest that mimicry has an as-yet-unknown structural or acoustic role in song, respectively. In these cases, mimetic accuracy does not matter; rather imitations and species-specific vocalizations are used in different ways. I explored these hypotheses using European starling (Sturnus vulgaris) song. Instead of testing the evolutionary functions of mimicry directly, I concentrated on the structural mechanics of mimicry in song. This approach allowed me to indirectly test whether mimetic and nonmimetic song components have the same functional effect. Chapter I is an overview of the more than 300 songbird species that are vocal mimics and shows that mimicry evolved repeatedly throughout the evolution of the songbird clade. The next three chapters are a detailed case study of the vocal mimicry of European starlings. In chapters II through IV, I use a combination of structural and acoustic analyses to emphasize the ways in which mimicry functions in starling song. I show that mimicry is treated differently from species-specific sounds, although in subtle, structural ways, and it remains unclear how important the inclusion of mimicry is to listeners.
Advisor: Daizaburo Shizuka