Bioacoustics of the Northern Elephant Seal

Vocal signaling plays an important role in the social interactions of many animals, and has the potential to convey biologically relevant information to receivers, including motivational cues (such as level of arousal or willingness to fight), and individual characteristics (such as identity, size, group association, and dominance status). This can be especially important during reproductive activities, as vocal signaling often mediates interactions between breeding partners, competitive rivals, and mother-offspring pairs. Our research group is currently working on understanding how northern elephant seals (Mirounga angustirostris) use acoustic cues to communicate biologically important information to one another during their annual breeding season. Specifically, we aim to examine how vocal cues are used to mediate competitive interactions during high stakes breeding activities.

Northern elephant seals have an extreme lifestyle both on land during their breeding season and while out at sea. They spend up to 8 months of the year foraging in the eastern and central North Pacific in between mating and molting, and may travel up to 10,000 km per trip. They are one of the deepest diving marine mammals in the world, and can dive up 1500 meters and hold their breath for up to 2 hours. Northern elephant seals breed annually during the winter months on islands and mainland rookeries along the western coast of the United States and Mexico. These animals maintain a highly polygynous breeding system in which adult males establish their dominance position within the colony in December and stay until mid-March, a period extending over three months without access to food or water. Competition between males is intense, with only a small subset of individuals ever gaining access to breeding females. While dominance relationships may be established through physical contact, these hierarchies are maintained through the use of stereotypic threat displays that include vocalizations and associated visual and seismic cues. These complex displays play an important role in settling otherwise costly interactions between competing males, as stereotyped acoustic signals often elicit appropriate behavioral responses from spatially separated individuals without physical contact.

The primary goal of this project is to examine the acoustic characteristics and functional significance of these male calls in order to improve our understanding of communicative behavior and the potential role of vocal learning in maintaining social structure in this species. In order to address some of these questions, we employ a comprehensive approach to our field efforts. We combine identification and marking, GPS re-sight data, behavioral observations, photometric analysis, playback experiments, and acoustic recording and analysis techniques to acquire detailed information about the behavioral and acoustic patterns exhibited by individuals animals. In doing so, we have confirmed that mature males have highly unique vocal signatures that are reliable within and between breeding seasons. These calls do not appear to vary significantly as a function of social context, suggesting that these threat vocalizations do not function to convey graded motivational cues to the listener. However, these stereotyped signals are extremely good indicators of individual identity, suggesting that males may use these cues to obtain information about their breeding rivals. Through acoustical analysis and playback experiments, we have found that these calls may not contain any honest information about that animal's size or dominance status. For example, not all dominant or large males possess similar call qualities such as call structure or duration. Instead, it appears that these individually unique threat vocalizations may serve as acoustic signatures by which other males learn to identify during the breeding season through learned associations. Future research will continue to explore the possible role of vocal learning in this species.

This is a collaborative project that includes researchers from the University of California Santa Cruz, Universite Paris Sud, and Universite Jean Monnet. The project is also made possible through the support of several undergraduate student researchers and interns. Research is conducted under the authorization of National Marine Fisheries Service Research Permit 14636 with oversight from the Institutional Animal Care and Use Committee at UCSC. All research is made possible through the support of the Ano Nuevo Natural Reserve and Ano Nuevo State Park.


 
Brandon Southall making source level measurements
Brandon Southall obtaining source level measurements from an adult male northern elephant seal during the breeding season.
 
Caroline Casey placing a temporary mark on a sleeping male
Caroline Casey uses hair dye to place a temporary mark on a resting seal.
 
A returning alpha male, 1C, vocalizing over his harem
The alpha male identified as 1C, calling over his harem on the north side of the Ano Nuevo mainland.
 
How to Get Involved
The Cognition and Sensory Systems Laboratory is supported by a team of hard working individuals, including research staff, graduate students, undergraduate research assistants, and interns. Volunteer research assistantships are typically offered to undergraduate students at UC Santa Cruz who work in the lab part-time year round. Internships last 3-4 months and are full time, unpaid, positions available to college students close to completing their degrees, or to those who have finished their degrees and intend to pursue post-graduate education in some form. Support for this project is usually needed between the months of December and March. For more information about research assistantships or internships, please write to Caroline Casey at pinnipedlab@gmail.com. The program seeks motivated individuals with background and/or interest in a variety of fields including biology, psychology, physics, engineering, environmental studies, computer sciences, and veterinary medicine.

More Information
Long Marine Lab is part of the Institute of Marine Sciences at UC Santa Cruz. The Seymour Marine Discovery Center at LML offers tours and additional information about the facility and ongoing research.
© 2017 Pinniped Cognition & Sensory Systems Laboratory. All rights reserved.