Scientists at UNSW Sydney have unveiled compelling new insights into the vocal behaviors of leopard seals in the remote and icy waters of Antarctica, revealing that these apex predators produce songs with a level of structural sophistication comparable to human nursery rhymes. This groundbreaking study, recently published in the journal Scientific Reports, explores how the underwater melodies of Hydrurga leptonyx exhibit a predictable patterning in temporal dynamics and complexity, a discovery that challenges long-held assumptions about animal communication in marine ecosystems.
Leopard seals are known as solitary hunters, ruling the Southern Ocean ice habitats as dominant predators. Yet, during the breeding season, male leopard seals engage in an extraordinary acoustic performance, singing underwater for extended periods that can last up to 13 hours daily. Their vocalizations occur in repetitive two-minute cycles involving two minutes submerged and two minutes at the surface to breathe — a grueling routine that underscores the biological significance of these songs. The research team, led by PhD candidate Lucinda Chambers, meticulously analyzed recordings collected decades ago using modern computational methods, revealing that these vocal sequences are far from random noise.
Entropy, a key concept in information theory quantifying the predictability or randomness of signal patterns, served as the primary analytical tool. When compared to an array of other animal vocalizations — including humpback whales, bottlenose dolphins, and squirrel monkeys — the leopard seal songs displayed an entropy value closely aligned with that of human nursery rhymes. This metric suggests a balance between repetition and variation optimal for communication efficacy, allowing the songs to be memorable yet unique enough to convey individual identity.
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The acoustic repertoire of leopard seals is constructed from a limited “alphabet” of just five distinct call types, which seem to be shared universally across the population. These calls themselves are indistinguishable in isolation, but each male arranges them in unique sequences, producing a signature pattern that functions much like a personal name. This sequence-based individuality implies a sophisticated level of vocal learning or patterning, where the relative order of calls, not mere acoustic variation, encodes identity information and potentially social status.
The broader ecological context of these findings is striking. The Southern Ocean presents a vast and acoustically challenging environment, with shifting sea ice platforms that leopard seals use as resting and breeding grounds. The underwater transmission of their song sequences across extensive distances enhances the likelihood of encounters between dispersed individuals, serving dual communicative functions. Males broadcast territorial claims to rivals while simultaneously advertising their physical fitness and genetic quality to potential mates, a dual signaling strategy that reflects complex selective pressures in extreme polar ecosystems.
The study draws intriguing parallels between the melodic structure of leopard seal songs and human musical constructs. Nostalgic nursery rhymes, characterized by their simplicity and predictability, provide a cognitive framework that facilitates memory and social bonding in humans. Similarly, the seals’ vocalizations balance repetition with a degree of variation, presumably optimizing them for long-range transmission in a noisy underwater soundscape and maximizing their biological effectiveness during a brief and energetically intense breeding window.
Historically, data for this study originated from extensive field efforts in the 1990s led by Professor Tracey Rogers, who developed innovative methods to capture discrete individual recordings. By marking individual seals with dye and returning at night to record their songs, the team established a valuable archive of analogue sound data. This retrospective approach allowed for the detailed analysis of individual vocal strategies and population-wide song characteristics long after the initial collection, highlighting the enduring scientific value of well-preserved bioacoustic datasets.
One of the remarkable discoveries is the extreme commitment male leopard seals display during the breeding season. Persistently diving and surfacing in a consistent two-minute singing cycle, these animals demonstrate a stamina and dedication reminiscent of terrestrial songbirds. This behavior not only underscores the physiological endurance required for such vocal displays but also suggests that acoustic performance is a critical component of reproductive success in this species.
From a biophysical standpoint, the stylization of these songs—marked by deliberate repetition of call sequences—is likely an adaptive response to the signal degradation typically encountered in underwater acoustic communication. Cold waters and the dynamic nature of pack ice environments impose constraints on sound propagation, favoring vocal signals that minimize ambiguity and maximize recognition at range. Simplified, patterned calls mitigate distortion effects, ensuring that key information reaches intended receivers despite environmental challenges.
Looking to the future, the research team intends to re-examine these unique Antarctic soundscapes with contemporary digital recording technology and advanced analytical algorithms. Such analyses will address whether the known five-call “alphabet” has undergone evolutionary changes in recent decades, whether novel call types have emerged, and if generational shifts impact the transmission of song patterns. Furthermore, the team aims to investigate whether leopard seal songs serve functions comparable to known signature whistles in dolphins, offering new perspectives on individual identity and social interaction protocols in marine mammals.
Overall, this research elevates our understanding of acoustic communication in polar marine predators, emphasizing the complex interplay between environmental constraints, evolutionary pressures, and behavioral strategies. By revealing surprising affinities between human nursery rhymes and leopard seal vocalizations, it challenges anthropocentric perspectives on the uniqueness of structured vocal behaviors and provides novel pathways for studying the cognitive and social lives of some of Earth’s most enigmatic animals.
Subject of Research: Leopard seal vocalization patterns and their structural similarities to human nursery rhymes
Article Title: Leopard seal song patterns have similar predictability to nursery rhymes
News Publication Date: 31-Jul-2025
Web References: https://www.nature.com/articles/s41598-025-11008-8
References: Scientific Reports, DOI: 10.1038/s41598-025-11008-8
Keywords: Animal sounds, Vocalization, Bioacoustics, Musical acoustics, Underwater acoustics, Mating success, Animal science, Animals, Animal communication, Behavioral ecology
Tags: animal communication in marine ecosystemsAntarctic wildlife acousticsapex predators in the Southern Oceanbreeding season behaviors of leopard sealscomplexity of leopard seal songsevolutionary biology of leopard sealsleopard seals vocal behaviorsnursery rhyme patterns in naturescientific study on animal communicationtemporal dynamics in animal songsunderwater melodies of leopard sealsUNSW Sydney research on seal songs