Humpback whales increase singing rate in response to seismic air guns

Seismic air guns, widely used in offshore resource exploration, are a major source of anthropogenic noise in marine environments. For some cetaceans, these impulsive sounds can disrupt acoustic communication critical for breeding and social interactions. Male humpback whales (Megaptera novaeangliae) produce long, highly structured songs as part of their reproductive display, often within areas overlapping seismic activity. This study investigated whether air gun noise alters the organisation and rate of humpback whale song. Four temporal parameters; inter-call interval, phrase duration, theme duration, song cycle duration, and one organisational variable (phrases per theme) were measured in the presence and absence of air gun pulses. Song cycle duration decreased by approximately 89 s during air gun exposure. Principal component analysis revealed two phrase categories, simple and complex, and showed that reductions in the repetition of complex phrases was the driver behind shorter theme and song cycle durations. Other parameters, such as inter-call interval and phrase duration, showed no consistent change, confirming that reduced complex phrase repetition was the main driver of song shortening. These findings provide evidence of a previously undocumented song-level response in singing humpback whales exposed to seismic air guns. They suggest that air gun noise may interfere with the production of complex song components, potentially distracting or confusing singers. Overall, this study highlights the need to consider sound type as well as amplitude when evaluating the effects of anthropogenic noise on marine mammals and demonstrates the vocal plasticity of humpback's vocal production in response to anthropogenic noise.