Cracking the code of leopard seal love songs

Leopard seals are often cast as sleek, thousand-pound hunters and Antarctic villains. To be honest, they aren’t social butterflies. For much of the year, they range alone over vast stretches of ice. However, when mating season arrives, instead of chasing penguins, they hang motionless beneath the ice. Instead of chasing mates across the floes, the males broadcast solos that drift for kilometers through the frigid water. Why? Because singing is a male leopard seal’s way to flirt, stake out territory, and quite possibly shout, “This patch of sea ice is mine!”

Underwater music contests

The musician side of leopard seals is the focus of a new Nature study from marine biologist Lucinda Chambers and colleagues John Buck and Tracey Rogers, published in Scientific Reports. Chambers, Buck, and Rogers combine the ecological expertise of UNSW Sydney’s Centre for Marine Science and Innovation with the pattern recognition know-how from the Department of Electrical and Computer Engineering at the University of Massachusetts Dartmouth.

Together they set out to answer a deceptively simple question: how predictable are a leopard seal’s songs?

The team analyzed the recordings of the “songs” of 26 wild males in Eastern Antarctica during breeding season, when each seal belts out hours-long sequences. To measure the order in those sequences, the team borrowed a concept called information entropy. Essentially, information entropy can be considered as a mathematical scale of surprise. High entropy means chaos, think of a jazz solo, full of twists. Instead, low entropy means you can guess what comes next.

What’s the music like?

When the researchers crunched hundreds of hours of recordings, they discovered something delightful: the seals’ songs are as predictable as human nursery rhymes. Not as spare as “Twinkle, Twinkle,” but far less random than whale arias or dolphin whistles.

Each seal strings together just five distinct call types, looping them in seemingly endless sequences. Imagine a composer writing an entire symphony using only five piano keys. Every song is assembled from only five trusty call types: high double trills, medium single trills, low descending trills, low double trills, and a hoot-plus-trill. The performance is literally broken into verses: a string of calls underwater, a quick surface breath lasting roughly two minutes (scientists mark this pause with a “Z”), and back down for the next stanza.

Why would a top predator use such tidy musical grammar? Streams of evenly spaced, familiar notes travel farther and degrade less in chilly saltwater, helping distant listeners pick out who is calling. For a species that might be tens of kilometers apart, clarity beats complexity. This is especially effective in an environment in which, during the mating season, females are bombarded by songs from all directions, considering that male leopard seals don’t just hum a quick tune: they can keep the set going for up to 13 hours a day.

In fact, the study hints that individual seals might encode a personal “signature” in the exact order of their calls, the same way you recognize a friend’s voice on the phone. So, if each crooner has his own motif, scientists could potentially track populations with underwater microphones instead of helicopters and tagging darts.

Vintage equipment, new analysis tools

Those recordings weren’t captured with modern digital gear. Instead, they were acquired using a 1990s cassette recorder and hydrophone, logging hours of songs between 1992-1994 and 1997-1998. They were only recently analyzed by the team with modern signal analysis techniques.

This research is a perfect example of how blending disciplines, in this case biology, acoustics, and information theory, can unlock new insights. It’s a case of science moving forward by listening closely to what nature has been saying all along.

If you want to learn more, the original article titled "Leopard seal song patterns have similar predictability to nursery rhymes" is available on Nature at https://www.nature.com/articles/s41598-025-11008-8.