Leopard seals’ sex life (almost) revealed
Thanks to the observation of a courtship ritual, we now know more about the sexual behaviour of the mysterious leopard seal. A mating process based on vocalizations that takes place far from the Antarctic ice.
For the first time, a team of researchers has observed a courtship interaction between two leopard seals. The results of this unprecedented observation were published on July 7 in Polar Biology.
This is not the first time that Dr. Sarah Kienle, a biologist at Baylor University in Texas, and her team have published a study on leopard seals. Sarah Kienle and her team have published a study on leopard seals. In 2022, research had already revealed more about the species’ movements and diving behaviors. Another study, published in 2023, established that leopard seals have the highest levels of the stress hormone cortisol among pinnipeds. This time, researchers focused on the reproductive behavior of this mysterious Antarctic predator.
For two hours, Dr. Kienle and her team observed a courtship between two leopard seals at Laguna San Rafael in Chile in December 2022. And to say the least, the interaction was highly vocal. Circling around an iceberg on which the female was lying, the male emitted 65 underwater calls in the form of high and low-pitched double trills, apparently addressed to his beloved. Low-pitched double trills were four times more frequent than high-pitched double trills. For her part, the female emitted seven calls in the form of muffled pulses, nasal puffs and grunts. After visual observation, the researchers recorded vocalizations over the following eight hours.
Another interesting element in this observation is the difference in the environment in which the male and female evolved during the courtship. While the male spent almost the entire observation time in the water, the female vocalized in the air from the piece of ice on which she was lying. This observation suggests a more passive role for the female in her sexual behavior.
However, the researchers were unable to establish whether the male was able to “close the deal”. Observation the following day revealed a laceration in the region of the genitals. According to the researchers, the male had attempted to mate with the female, and either she or another leopard seal had caused the injury.
This observation marks an important step forward in our knowledge of this marine mammal, which is difficult to observe in its natural environment. “Together, we find that leopard seal courtship involves a suite of behavioral and acoustic behaviors by both sexes, both in air and under water. “, note the authors in their study. “This is the first description of leopard seal sexual behavior in the wild. Our study also provides the first evidence that leopard seals mate in South America.”
For a long time, it was thought that leopard seals needed sea ice to reproduce. However, various studies, including one involving 19 newborns, have shown that not only were the majority of births not carried out on the ice, but that they could also take place outside Antarctica. The observation of this courtship in southern Chile therefore points in the direction of non-Antarctic breeding: “These data provide additional evidence that leopard seals can – and are – breeding outside of Antarctic pack ice.”, notes Dr. Kienle in a press release published by Baylor University on July 17.
While this observation has enabled us to learn more about the sexual behavior of leopard seals, it still raises a number of questions, notably concerning the choice of females in mating behavior, or the question of competition and territoriality and the role they play in the species’ reproduction. Questions that the researchers hope to answer in the future with further observations and the collection of acoustic and video data.
Mirjana Binggeli, Polar Journal AG
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