New research suggests that the intricate songs of male humpback whales are directly influenced by their diving patterns. A study, which is the first to connect an entire humpback whale song structure to a complete dive cycle, utilized data from suction-cup attached recording tags to establish this link. The findings could enable scientists to infer whale behavior solely from acoustic recordings.
The haunting and complex songs of male humpback whales are crucial for reproduction during the winter breeding season, can last for hours, and travel for miles underwater. While the sounds of these songs have been studied for decades, understanding what the whales are physically doing while singing has been less clear. The connection between singing and physical activity could offer insights into how singing impacts a whale's energy expenditure, oxygen management, and susceptibility to underwater noise and vessel strikes.
Dr. Julia Zeh's research, published in the journal Current Biology, identified a previously unrecognized relationship between the structure of humpback whale songs and the animals' movements. The study indicates that specific song components, known as themes, are consistently associated with particular stages of a dive. To collect the data, Dr. Zeh and her team attached sound-and-movement recording tags to singing humpback whales off the coast of Maui over a six-year period, from 2018 to 2024.
These non-invasive tags, roughly the size of a tablet, were affixed to 16 whales using long poles and, more recently, drones. The tags recorded both the whale's underwater sounds and its movements before detaching, allowing researchers to retrieve the devices and analyze the data. Some whales were observed to repeat their songs continuously for up to 16 hours.
Song Themes and Dive Cycles
The research found that recurring song themes aligned consistently with specific parts of a dive. While previous observations noted that certain themes appeared as whales approached the surface, this study is the first to link the complete song structure to the entire dive cycle. Dr. Zeh suggests this connection implies more than mere coincidence. Themes sung while whales maintained a stable depth during the deepest part of a dive exhibited different variability compared to themes sung at other depths. This suggests these sections might be more strongly shaped by sexual selection, potentially serving as indicators of a male's individual quality.
Conversely, themes associated with other parts of the dive may be influenced by physiological or environmental factors, such as the challenges of managing oxygen and buoyancy while singing. Dr. Zeh stated that these findings provide a direction for investigating which song parts are likely driven by sexual selection, noting that variations concentrated near a whale's deepest points may be where a male's song is working hardest to stand out.
Potential Applications for Conservation
The study's findings also have practical implications for whale research and conservation. Acoustic monitoring is a common method for tracking whale populations. By understanding the relationship between song and movement, scientists could potentially determine a whale's depth or position directly from audio recordings. This could help establish a clearer baseline for normal humpback whale behavior, which is essential for identifying disturbances caused by human activities like shipping traffic or ocean noise.
It remains an open question whether these patterns apply to humpback whale populations outside of Hawaii. Dr. Zeh anticipates that similar physiological constraints would likely exist globally, but differences in song evolution between hemispheres could mean different populations face distinct pressures on their song structure. Further research involving comparable tag data from singing whales on breeding grounds worldwide would be needed to confirm this.
Dr. Zeh conducted this research during her doctoral studies at Syracuse University, where she developed the skills to combine bioacoustic analysis with biologging technology. She credits her time at Syracuse with expanding her understanding of the possibilities within the field and providing the foundation for her current work in ecological monitoring and conservation.