Effect of Morphology and Spatial Distribution of Males on Vocal Identity in a Non-Learning African Wood Dove.

Individual vocal signatures are widespread across animal taxa, yet the processes underlying their emergence remain poorly understood. Vocal individuality may arise incidentally from morphological variation or be shaped by social environments in which reliable recognition reduces interaction costs. Here, we investigated these non-exclusive alternatives in the Emerald-spotted Wood Dove (Turtur chalcospilos), a territorial, non-learning bird inhabiting African savanna woodlands. We quantified vocal individuality across multiple song units and tested whether acoustic variation covaried with male morphology (body size and bill dimensions) and spatial factors, including geographic distance and number of neighbors, reflecting the intensity of territorial interactions. If social pressures enhance recognition efficiency, we predicted greater acoustic dissimilarity among close neighbors and in denser neighborhoods, together with greater within-individual vocal consistency. Although songs were highly individually distinctive, morphological traits explained only a small portion of the acoustic variation, indicating that individual signatures cannot be reduced to simple biomechanical constraints. Contrary to our prediction, acoustic dissimilarity increased with geographic distance, and nearby males were more acoustically similar. Spatial effects on individual vocal consistency were weaker, although males with closer neighbors tended to show lower within-individual variation. Local male density showed no consistent effect on either pattern. These results suggest that vocal individuality in this non-learning species is more associated with spatial relationships among territorial males than with morphometric traits or competitor density. By disentangling morphometric and spatial influences, this study refines our understanding of how individual identity signals can emerge and persist in territorial systems without vocal learning or complex social structure.