Air–water interface calling behavior of southern right whales ( <i>Eubalaena australis</i> ) in Península Valdés, Argentina: A sound production–based approach

We describe an air-water interface calling behavior observed in southern right whales (SRWs; Eubalaena australis) in Golfo Nuevo, Península Valdés, Argentina. This behavior involves SRWs producing audible vocalizations at the surface, here termed "interface vocalizations" (IFVs), which propagate simultaneously in-air and underwater. IFVs were documented through opportunistic visual observations combined with synchronized in-air and underwater recordings, complemented by citizen science videos. Twenty IFVs were recorded across eight events, with ten including fully synchronized acoustic data. Both in-air and underwater components are tonal, low-frequency signals with different harmonic structures and variable duration, perceived in air as "foghorn"-like sounds. Behavioral and acoustic analysis indicates that IFVs are intentionally produced, voluntarily controlled, non-breathing-related vocalizations. All callers were adult whales observed across simple and complex social contexts. The findings support IFVs as a distinct sound category from those previously described for SRW, with anatomical production likely mediated by the laryngeal apparatus. These results highlight the plasticity of SRW acoustic behavior and the complexity of its sound production, raising questions about the potential biological, communicative, and adaptive roles of IFVs in dual-pathway signaling.