The short version
- Researchers at Syracuse University tagged 16 singing male humpbacks off Maui between 2018 and 2024 and recorded sound and movement together.
- Specific themes in the song lined up with specific phases of the dive, the first time an entire song has been mapped onto a full dive cycle.
- Themes sung at the deepest point varied in ways that suggest sexual display, while others look constrained by oxygen and buoyancy.
A male humpback sings with his mouth closed, underwater, while holding his breath. Every phrase costs him oxygen he cannot replace until he surfaces, and every change of depth changes the pressure on the air he is pushing around inside his body. That is a strange set of conditions for a composer, and a study published in Current Biology in August suggests the song has been written around them.
The study
Julia Zeh and colleagues in Susan Parks’ bioacoustics lab at Syracuse University attached suction-cup tags to 16 singing male humpbacks in the waters off Maui between 2018 and 2024. The tags recorded sound and movement at the same time, so for the first time the researchers could line up what a whale was singing with where he was in the water column and what his body was doing. Some of the whales sang continuously for up to 16 hours.
The result: particular themes in the song aligned with particular phases of the dive. A humpback song is built from repeated themes, and the study found that where a theme falls in the song tracks where the whale is in the descent, the bottom and the ascent. It is the first time a whole song has been mapped onto a whole dive cycle.
Three constraints on a singer
Pressure is the first. Every 10 meters of seawater adds roughly one atmosphere. Air inside a whale compresses as it dives, so the same volume of air that fills a chamber near the surface occupies a fraction of that space at depth. Whatever sound-producing anatomy the whale is using, the air it has to work with changes with every meter.
Buoyancy is the second. A lungful of air near the surface makes the whale float; compressed at depth, it floats him less. Holding position, rising or sinking all take different amounts of work at different depths, and the work competes with singing for the same breath.
Breath is the third, and it sets the clock. A song must fit inside a dive, and the dive must fit inside the oxygen the whale brought down. The study’s authors read some themes as shaped by exactly this: oxygen and buoyancy management constrain what can be sung and when.
The part that is display
Not every theme answered to physics. The themes sung at the deepest point of the dive varied differently from the rest, in a way the researchers interpret as a sexual-selection signal: a part of the song where the singer can show something about himself rather than simply manage his air. If that holds, the humpback song is two things braided together, an engineering solution and an advertisement, and the dive tells you which is which.
What to listen for
Recordings of humpback song rarely come with depth data, so the dive structure is invisible to a listener. What you can hear is the repetition: themes returning in order, cycle after cycle, for hours. Now you know that each cycle was a trip down and back, and that the deepest note was the one the singer chose to spend his breath on.
