At nightfall, the Antarctic sky is adorned with pink nuances. The male sea leopard then emerges, leaving the ice to sink into cold waters. There he spent the night singing underwater, surrounded by floating ice.
For almost two months, he starts again each evening. His songs resonate so hard that the ice vibrates around him. Each song, composed of trilledtrilled and hululating, follows a precise diagram.
In a world premiere, we have analyzed these songs and found that the structure of their patterns is surprisingly like that of human nursery rhymes.
We believe that this is an intentional strategy. Although these seals are lonely, males need their song porteporte On large icy expanses to seduce a partner.
A season of underwater solos
Sea leopards, Hydrurga leptonyxHydrurga leptonyxtake their name from their spotted coat. They live on ice and in the surrounding waters of Antarctica.
They are particularly noisy during the breeding season, which extends from the end of October to early January. A female seal sings a few hours during its heat periods, but it is the males who are the real stars.
Male sea leopards emit acute tries similar to those of crickets. © Ryanbusiness
Every night, they embark on underwater solos that can last until 1 p.m. They plunge into the sea, sing underwater for about two minutes, then turn surface to breathe and rest. This demanding ritual is repeated for weeks.
A male seal weighs approximately 320 kilogramskilogramsbut produces surprisingly acute trills, similar to those of a small cricket.
Within a population of sea leopards, the sounds themselves do not vary in terms of tone or durationduration. But the order and the diagram in which these sounds are produced vary considerably from one individual to another.
Our research has analyzed these individual songs, which we have compared to those of other singers animals, and even to human music.
Listen to sea
The data used in this study were collected by one of the authors of this article, Tracey Rogers, in the 1990s.
Aboard her quad, Ms. Rogers crossed the ice floeice floe Antarctica to the seaside and marked 26 male seals using a dye during their sleepsleep. She then returned to record their songs nocturnalnocturnal.
Recent research has made it possible to analyze these recordings to better understand the structure and patterns of their songs. We measured “theentropyentropy From their sequences. Entropy measures how predictable or random is predictable.
We found that the songs consisted of five main sounds.
A surprisingly predictable scheme
We then compared the songs of sea leopards with several stylesstyles Human music: baroque, classic, romantic and contemporary, as well as songs of Beatles and nursery rhymes.
What struck us is the similarity between the predictability of human nursery rhymes and the songs of sea leopards. The nursery rhymes are simple, repetitive and easy to memorize: exactly what we find in the songs of sea leopards.
The range of entropy was comparable to that of the 39 nursery Golden Song Booka collection of words and partitionspartitions For classic children’s songs, published for the first time in 1945. It includes English classics like:
- Twinkle, Twinkle, Little Star (Ah! Will I say, Mom)
- Brother Jacques
- Ring Around a Rosy
- Baa, Baa, Black Sheep
- Humpty Dumpty
- Three Blind Mice
- Rockabye Baby
For humans, the foreseeable structure of a nursery melody helps to make it simple enough for a child to be able to learn it. For a sea leopard, this predictability could allow him to learn his song and repeat it for several days in a row. This consistency is important because changes in tone or frequency can cause misunderstandings.
Such as hawkhawksea leopards could also use their songs to distinguish themselves from others and report their ability to reproduce. A larger structure in the songs helps to ensure that listeners receive the message correctly and can identify who sings.
An evolving song?
The songs of sea leopards may seem very different from those of humans. However, our study shows that the complexity and structure of their songs are remarkably similar to those of our nursery rhymes.
Singing communication is very common behavior in animals. However, the structure and predictability of songs in mammalsmammals were only studied in a few speciesspecies. We know little about what motivates them.
Understanding animal communication is essential. This can improve animal conservation and well-being efforts, while providing valuable information on their cognitioncognition and their evolution.
Since the recordings made in the 1990s, technology has evolved considerably. In the future, we hope to return to Antarctica to record and study more, in order to better understand if new types of calls have appeared and if the Songs of the Songs of Leopards de Mer evolve over the generations.