Thursday, November 13, 2025

Monk seal acoustic breakthrough: Hawai’i study quadruples known call types and detects novel communication strategy

UH Mānoa-Led research reveals 25 call types and a never-before-heard "combinational" communication strategy in seals

University of Hawaii at Manoa

Two monk seal underwater — image:
Two adult Hawaiian monk seals interacting under water.
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Credit: Krista Jaspers

New research led by UH Hawaiʻi Institute of Marine Biology (HIMB) Marine Mammal Research Program (MMRP) has drastically increased our understanding of Hawaiian monk seal (Neomonachus schauinslandi) underwater sound production, revealing a vocal repertoire far more complex than previously described. Published today in Royal Society Open Science, the study analyzed thousands of hours of passive acoustic data and identified 25 distinct underwater vocalizations, a dramatic increase from the six calls previously known from seals in human care. The team also found that Hawaiian monk seals produce these low-frequency calls throughout the day, with consistent vocal types detected across the Hawaiian Archipelago and higher calling rates at sites with greater seal abundance. This breakthrough discovery establishes a baseline for understanding the acoustic world of this highly endangered and endemic Hawaiian species.

Key Discoveries of a Hidden World

"We discovered that Hawaiian monk seals—one of the world’s most endangered marine mammals—are far more vocal underwater than previously known," shares Kirby Parnell, lead author of the study and a PhD candidate with MMRP. "By analyzing over 4,500 hours of recordings from across the Hawaiian Archipelago, we identified more than 23,000 vocalizations representing at least 25 distinct call types."

The study, which deployed passive acoustic recorders at five key monk seal habitats from Molokaʻi to the remote Northwestern Hawaiian Islands, uncovered:

Expanded Vocal Repertoire: Researchers identified 20 previously undocumented calls.
Novel Communication Strategy: The research provides evidence that monk seals can combine different vocalizations together, creating “combinational calls”—a communication strategy never before reported in any pinniped species.
A Foraging Call: The team discovered one novel elemental call type, the Whine, produced during foraging, representing only the second known example of a seal species using vocalizations while pursuing prey.

"We were surprised by the sheer diversity and complexity of monk seal vocalizations,” notes Parnell. “The discovery of combinational calls, where seals link multiple call types together, suggests a previously unknown level of complexity in pinniped acoustic communication. Finding a new call type—the Whine—associated with foraging behavior was also unexpected and suggests that monk seals may use sound not only for mating or socializing, but possibly for foraging purposes as well."

Implications for Conservation in Hawaiʻi

The Hawaiian monk seal is Hawaiʻi’s only endemic marine mammal and a treasured part of Hawaiian culture. This research is vital for the species' conservation, particularly in the face of increasing ocean noise.

"This research provides the first comprehensive description of free-ranging Hawaiian monk seal underwater sound production, an important step toward understanding how they use sound for critical life-history events," explains Lars Bejder, Director of MMRP, Professor at HIMB, and co-author of the study. "Because their vocalizations overlap with the same low-frequency range as many human-generated sounds (e.g. vessel noise), this work also helps us evaluate how ocean noise may affect communication, reproduction, and behavior in this endangered species."

These results lay the foundation for using passive acoustics to monitor monk seal populations across their vast range and to protect their acoustic habitats as human activity persists in Hawaiian waters. Future research will decisively link these documented vocalizations to specific Hawaiian monk seal behaviors, such as foraging, swimming, social interactions, and reproduction. A critical next step involves developing automated detection systems to monitor the seals' acoustic activity more efficiently and non-invasively, providing a powerful, long-term tool for conservation management and ecological understanding.

About the Research Team

The interdisciplinary research team included graduate students, undergraduate students, and recent alumni from the University of Hawaiʻi at Mānoa, as well as coauthors from France and the Pacific Islands Fisheries Science Center’s Hawaiian Monk Seal Research Program.

“Manually annotating over 23,000 calls by hand is no small feat, and I have a team of interns to thank for helping with the analysis!” shares Parnell. “This research would also not have been possible without the support of the Hawaiian Monk Seal Research Program, who deployed and retrieved the acoustic recorders in the Papahānaumokuākea National Marine Sanctuary.”

This work was supported by NOAA Fisheries via the Cooperative Ecosystem Studies Unit (CESU) award NA19NMF4720181.

Journal

Royal Society Open Science

Method of Research

Observational study

Subject of Research

Animals

Article Publication Date

11-Nov-2025

A Hawaiian monk seal takes a snooze.

Credit

Fabien Vivier

The passive acoustic recorder, SoundTrap 500, deployed at Kaluapapa, Moloka’i, was used to capture ocean sounds.

Credit

Griffin Hoins

Shouting at seagulls could stop them stealing your food

University of Exeter

Shouting at seagulls makes them more likely to leave your food alone, research shows.

University of Exeter researchers put a closed Tupperware box of chips on the ground to pique herring gulls’ interest.

Once a gull approached, they played either a recording of a male voice shouting the words, “No, stay away, that’s my food”, the same voice speaking those words, or the ‘neutral’ birdsong of a robin.

They tested a total of 61 gulls across nine seaside towns in Cornwall and found that nearly half of those gulls exposed to the shouting voice flew away within a minute.

Only 15% of the gulls exposed to the speaking male voice flew away, while the rest walked away from the food, still sensing danger.

In contrast, 70% of gulls exposed to the robin song stayed near the food for the duration of the experiment.

“We found that urban gulls were more vigilant and pecked less at the food container when we played them a male voice, whether it was speaking or shouting,” said Dr Neeltje Boogert of the Centre for Ecology and Conservation at Exeter’s Penryn Campus in Cornwall.

“But the difference was that the gulls were more likely to fly away at the shouting and more likely to walk away at the speaking.

“So when trying to scare off a gull that’s trying to steal your food, talking might stop them in their tracks but shouting is more effective at making them fly away.”

The recordings, in which five male volunteers recorded themselves uttering the same phrase in a calm speaking voice and, separately, in a shouting voice, were adjusted to be at the same volume, which suggests gulls can detect differences in the acoustic properties of human voices.

“Normally when someone is shouting, it's scary because it's a loud noise, but in this case all the noises were the same volume, and it was just the way the words were being said that was different,” said Dr Boogert.

“So it seems that gulls pay attention to the way we say things, which we don’t think has been seen before in any wild species, only in those domesticated species that have been bred around humans for generations, such as dogs, pigs and horses.”

The experiment is designed to show that physical violence is not necessary to scare off gulls, and the researchers used male voices as most crimes against wildlife are carried out by men.

“Most gulls aren’t bold enough to steal food from a person, I think they’ve become quite vilified,” said Dr Boogert.

“What we don't want is people injuring them. They are a species of conservation concern, and this experiment shows there are peaceful ways to deter them that don't involve physical contact.”

“Herring gulls respond to the acoustic properties of men’s voices” is published in Biology Letters.