The acoustic discrimination and recognition of individual heterospecifics by humans: proximate and ultimate causes

Humans readily discriminate and recognize others by their voices, but it has not yet been studied whether this is also possible with the vocalizations of individual non-primates. My thesis addresses this question from both the proximate and ultimate perspective. In Chapter 1, I introduce the mechanism behind the individual discrimination of conspecific and heterospecifics by their vocalizations. Using a comparative approach, the physical properties of vocalizations and individual voices, their production and perception by species across the amniote clade are discussed. Three experiments are presented to examine whether humans can discriminate individual zebra finches by their songs with and without pitch contour, as well as individual large-billed crows by their calls. In Chapter 2, I focus on the functions associated with individual recognition through vocalizations and what fitness benefits this may entail, specifically in the context of reciprocal altruism between heterospecifics. A fourth experiment assesses the acoustic recognition of individual crows by humans in an altruistic exchange situation. In Chapter 3, I employ a theoretical approach reviewing the phylogenetic history of the focal species and their last common ancestor with a focus on their respective vocalizations. Taken together, these three sections provide further insights into the evolution of amniote vocalizations and the perception of identity across species.