Knowing a <i>kurr</i> from a <i>korrr</i>: acoustic signatures of the sexes are encoded in duets of the monomorphic Sarus Crane (<i>Antigone antigone</i>)

Species without external sexual dimorphism have evolved alternative techniques to recognise and signal sex-specific traits. Socially cohesive species utilise vocal communication to express territoriality and encode the acoustic signatures of each sex. We examined the feasibility of using acoustic cues to identify the contribution of each sex in the duets of the monomorphic Sarus Crane, a large waterbird famed for its pair bond. We analysed 215 duets from 136 pairs across north Indian farmlands and derived 24 note-level and 28 duet-level measurements. We reduced dimensions with Principal Component Analysis and used mixed-effect models to find male and female duet contributions with substantial temporal disparities. We used generalised linear mixed models to evaluate the accuracy of sex assignment using acoustic characteristics of the notes and found that main notes were the most reliable (<i>N</i> = 2082, 81% accuracy), with introduction notes (<i>N</i> = 516, 75%) and trill notes (<i>N</i> = 427, 65%) having relatively lower reliability. Male notes were longer, with broader bandwidth and higher modulation, whereas female notes were shorter, higher-pitched, and characterised by a more asymmetric spectrum, narrower bandwidth, and lower modulation. The Sarus Crane duets effectively transmitted sex signatures acoustically offering a reliable non-invasive method for sex identification with potential benefits for research and management efforts.