Spectral interleaving by singing humpback whales: Signs of sonar

Abstract

Singing humpback whales produce a wide variety of tonal and broadband units within their songs, usually organized into patterned sequences. Here, an extensive database of songs made available through Google's Pattern Radio website was analyzed to test the hypothesis that singers produce consecutive units in ways that minimize overlapping spectral content. Consistent with earlier analyses, singers maintained spectral separation across units within most repeating patterns (phrases and subphrases). Additionally, singers preserved the continuity of concentrated spectral energy, as well as the timing of units, as they cycled through different themes. Within songs, singers alternated between producing units that generated persistent reverberant tails tightly focused within narrow frequency bands and more impulsive, broadband units. By spectrally interleaving units, singing humpback whales can potentially avoid overlap between units that could interfere with auditory reception of the signals. By producing signals with broadband and narrowband elements that are spectrally and temporally segregated, singers may also maximize the distances at which they can detect and localize targets using echoes from those signals.