Eavesdropping on a humpback whale male’s song can provide information on its physical and reproductive condition

In species in which individuals of the same sex produce the same calls, variability in call production may provide key information on an individual’s physical and reproductive fitness. Humpback whale males are well known for producing complex vocalizations termed song, with all males from the same region producing the same song. Using a suite of data collected from male singers in the Maui breeding grounds in 2018–2019 including body length, blubber testosterone concentration, and song unit acoustic measurements at established distances, we first determined that body length was positively correlated with testosterone concentration, even when controlling for ordinal day of measurement (r = 0.74 (df = 4), p = 0.046). Next, we constructed linear mixed-effects models for each song unit type separately to test whether body length also predicts various acoustic parameters. Across six unit types, larger males consistently produced song with lower mean peak frequency (p 0.001). Other acoustic parameters such as source level and unit duration varied significantly in their relationship to body length depending on the song unit. These results demonstrate that listening whales can potentially derive key information on both a male’s physical and reproductive conditions based on its song.