Seal singers in Antarctica: From love songs to ultrasonic vocalizations

Seals are among the most fascinating creatures to call Antarctica’s icy waters and shores home. Their remote, vast habitat makes studying them a real challenge, and scientists are only beginning to uncover the secrets of these elusive animals. Among the most intriguing mysteries? Their haunting, otherworldly vocalizations.

We’ve heard about the enchanting songs of humpback whales and the clicks and whistles of dolphins. But seal sounds are unlike anything else—eerie, almost alien tones that echo through the frigid waters.

For seals and many other marine animals, sound is essential. Unlike in the air, sound travels nearly five times faster underwater, making it the ideal way to send signals across vast distances. Seals use these vocalizations for multiple purposes—communication with one another, navigation through murky waters, and locating food. With finely tuned hearing, these animals are masters of underwater acoustics, and their “voices” offer a glimpse into a world still largely hidden from us.

Are Weddell Seals the best seal singers?

Weddell seals are among the best-studied seal species in Antarctica. Each spring, female Weddell seals haul out onto the land-fast ice of Erebus Bay in the Ross Sea to give birth. This breeding population has been observed and studied since the 1960s.

These seals are particularly famous for their remarkable vocal repertoire, which includes chirps, whistles, trills, chugs, and buzzes, among other sounds. Some calls are territorial, with males producing distinct sounds to establish underwater territories and attract mates during the breeding season. Other calls, for example, are used in aggressive contexts. Vocalizations can vary from 10-20 ms for clicks to over a minute for trills.

Weddell seals can vocalize both under and above the water. They typically haul out on land-fast ice – and even when lying on the ice, they can hear conspecifics’ vocalizations coming from below the surface. In the past, researchers doubted this because they did not yet understand how well seals could hear in the air.

From a personal standpoint, I’m not sure if Weddell seals hold the title of Antarctica’s best seal singers, but hearing one vocalize during a rare encounter onshore is truly unforgettable. I wish we knew a lot more about the meaning of their vocalizations. 

Echolocation in seals?

Dolphins, other toothed whales, and bats use echolocation to navigate and find food by producing sound waves that bounce back when they reflect off objects. For a long time, scientists believed seals lacked this ability—but Weddell seals might be challenging that assumption.

A few years ago, researchers at McMurdo Station in the Ross Sea, Antarctica, installed the McMurdo Oceanographic Observatory (MMO). Situated 21 meters below the sea ice of McMurdo Sound at 78° south, the MMO used a camera, hydrophone, and other sensors to collect real-time data.

Over its two years of operation, the MMO frequently detected ultrasonic frequencies. Analysis revealed that 17% of the seals’ calls, including nine distinct types of tonal vocalizations, reached frequencies as high as 50,000 Hz. For comparison, human hearing typically ranges from 20 to 20,000 Hz, though it diminishes with age. Weddell seals, however, are thought to perceive sounds up to 60,000 Hz.

Weddell seals remain in the Southern Ocean year-round and are the only mammal to live and breed so close to the South Pole. If they do use echolocation, this ability could help them navigate beneath the sea ice during the pitch-black Antarctic winter. Alternatively, these high-frequency vocalizations might serve as a form of communication between individuals.

Researchers still don’t know whether these sounds are produced by males, females, or specific age groups, but future studies may provide more insight into the purpose of Weddell seals’ ultrasonic calls.

Crabbies, leopards, and Ross seals

Harbor seals produce over 50 distinct vocalizations, but researchers know even less about the vocalizations of other Antarctic seal species.

Recently, a video surfaced on Instagram showing a vocalizing leopard seal on a pier, likely in New Zealand. This rare footage provides a glimpse of what these elusive animals sound like.

Interestingly, older leopard seals produce higher-frequency calls, a pattern that defies expectations, as larger, older animals typically vocalize at lower frequencies. Older male leopard seals, in particular, demonstrate impressive stamina, singing repeatedly as a display of strength that can be heard from a distance. While female leopard seals also produce song-like calls, males are more persistent, often singing nightly for months. The purpose of this behavior remains a mystery.

For Crabeater seals, or “crabbies,” vocal activity peaks during their breeding season in late October and November. Like many Antarctic seals, their vocalizations occur primarily at night.

The Ross seal, the most enigmatic of Antarctic seals, also vocalizes predominantly at night. Few people have ever seen a Ross seal in the wild, but acoustic monitoring has shed light on their movements in the Southern Ocean, including evidence of a northward migration.

A Look Beyond Antarctica

Seals in other parts of the world are more accessible for scientists and therefore a lot easier to study. Cape fur seals, for example, inhabit the Southern tip of the African continent, the Southeast of Australia, and Tasmania where they breed in huge colonies of up to 1,500 individuals. Imagine all the noise! Yet, these seals have found ways to communicate effectively. Their vocalizations, for example, contain information about the age and sex of the individual for easier recognition in their noisy environment. 

Communication between mothers and pups is especially critical. Female Cape fur seals embark on foraging trips at sea, leaving their pups onshore. Upon returning, they use unique calls to reunite with their young, ensuring the bond remains strong even after separation.

Vocalizations are also important for interactions between males. Males Cape fur seals produce barks that vary in rate and frequency depending on their arousal state, i.e. whether they are excited or relaxed. This “vocal code” likely helps reduce conflicts during the breeding season, minimizing the risk of injury. Males can also differentiate neighboring males from stranger males, responding more aggressively to the vocalizations of strangers.

Who knows just how much more we’ll uncover in the future? Recent breakthroughs in fields like machine learning and bioacoustics are already helping us decode animal sounds, movements, and behaviors. Imagine the possibilities! With AI advancing rapidly, we may one day be able to directly translate animal communication into human language. Can you picture that?

And I’m sure it wouldn’t just be “nice things” animals would have to share with us! This new understanding could transform our perception of animal sentience and bring monumental changes to the way we approach animal rights and conservation. The impact could be revolutionary, reshaping our connection to the natural world.

Sources and further reading

• Thomas, J. A., Awbrey, F. T., & Fisher, S. R. (1983). Incidental evidence for echolocation in polar pinnipeds. The Journal of the Acoustical Society of America, 74(S1), S75-S75.
• Oetelaar, M. L., Terhune, J. M., & Burton, H. R. (2003). Can the sex of a Weddell seal (Leptonychotes weddellii) be identified by its surface call?. Aquatic Mammals, 29 (2), 261-267.
• Klinck, H., Mellinger, D. K., Klinck, K., Hager, J., Kindermann, L., & Boebel, O. (2010). Long-range underwater vocalizations of the crabeater seal (Lobodon carcinophaga). The Journal of the Acoustical Society of America, 128(1), 474-479.
• Terhune, J. M. (2017). Through-ice communication by Weddell seals (Leptonychotes weddellii) is possible. Polar Biology, 40(10), 2133-2136.
• Cziko, P. A., Munger, L. M., Santos, N. R., & Terhune, J. M. (2020). Weddell seals produce ultrasonic vocalizations. The Journal of the Acoustical Society of America, 148(6), 3784-3796.
• Martin, M., Gridley, T., Harvey Elwen, S., & Charrier, I. (2021). Vocal repertoire, micro-geographical variation and within-species acoustic partitioning in a highly colonial pinniped, the Cape fur seal. Royal Society Open Science, 8(10), 202241.
• Martin, M., Gridley, T., Elwen, S. H., & Charrier, I. (2022). Feel the beat: cape fur seal males encode their arousal state in their bark rate. The Science of Nature, 109(1), 5.

Are you curious about the sounds that come out of animal’s mouths? Check out the Audio Gallery – Discovery of Sound in the Sea for sounds of a variety of marine animals, including many seals!