Sex Differences in Turtle Vocalizations Reflect Social Context and Behavioural Roles

Acoustic communication is widespread in animals, yet its function in turtles remains poorly understood. Although turtle signaling has been considered primarily visual and chemical, many species vocalize across life stages. We investigated adult vocalizations in the Midland Painted Turtle ( Chrysemys picta marginata ) to test whether call types and acoustic traits vary across social contexts. We recorded behavior and vocalizations during 35 hours of 1-hour trials involving solitary individuals and paired interactions (male–male, female–female, and mixed-sex). We identified five distinct call types, including one produced exclusively by males. Acoustic traits varied across social contexts, and males exhibited greater within-individual trait variance than females, although some males experienced different pre-treatment conditions that may have affected vocalization patterns. While we cannot definitively identify vocalization function, theory suggests greater within-male variation may also reflect condition-dependent signaling under intrasexual selection. Additionally, vocalization rates were negatively correlated with the number of close social interactions, suggesting that vocalizations are used at a distance, while visual, tactile, or potentially chemical cues dominate at close range. Our findings push forward our understanding of vocalization types, bimodality of turtle communication, and vocalization function, identifying many exciting pathways for further investigation.