Possible vocal coordination by co-singing humpback whales: More signs of sonar

Active position estimation involves localizing and tracking one or more targets. Like most mammals, cetaceans can estimate positions by listening to vocalizations. Current hypotheses of whale song function universally assume that listeners can track the origins of songs but few address how listeners do this. Actively tracking sources may be particularly challenging when multiple overlapping songs are audible. Recent analyses show that singing humpback whales within choruses dynamically modulate spectral features of songs in ways that may enhance the detectability and localizability of singers as well as echoes generated by songs. Spectral modulation by co-singing humpbacks appears to be context dependent, suggesting intermittent vocal coordination between singers. Solo singers spectrally interleave units in ways that reduce potential interference. Preliminary results suggest that dyadic singers may similarly shift the spectral content of units in real time to minimize spectral convergence. The sonar hypothesis for song function is the only hypothesis that predicts singers can benefit from morphing the spectral content of units within songs and from modulating song overlap in the frequency domain.