Walrus Acoustics

Overview

Pacific walruses (Odobenus rosmarus divergens) produce a surprisingly complex vocal repertoire during social interactions at haul-out sites. Sounds range from low-frequency grunts and bellows to remarkable underwater bell-like calls that can carry across considerable distances. Understanding the function of these vocalizations requires linking acoustic properties—frequency, duration, temporal pattern—to the behavioral context in which they occur.

This experiment drops you into a crowded arctic haul-out where dozens of walruses are vocalizing simultaneously. Your job is to make sense of the noise.

What You'll Do

Listen to walrus calls in a simulated arctic haul-out environment. View spectrograms of each vocalization as it occurs. Categorize calls by type—grunt, bellow, knock, bell, and whistle—based on their acoustic signatures. For each call, record the behavioral state of the calling individual (resting, moving, aggressive display, courtship, or mother-pup interaction).

Over the course of the session, you'll build a vocal repertoire catalog that links each call type to its behavioral context. Are bellows associated with aggression? Do bell calls occur primarily during courtship? Does the frequency range of a call predict the caller's body size? These are the questions your data will address.

Learning Objectives

1. Read and interpret spectrograms, identifying key features like fundamental frequency, harmonics, and temporal structure
2. Build a vocal repertoire catalog for a marine mammal species
3. Test hypotheses about call function using correlational data between call type and behavioral context
4. Practice acoustic measurement techniques (duration, frequency range, repetition pattern)

Background

Marine bioacoustics is a rapidly growing field, driven partly by concerns about anthropogenic noise and partly by new recording technologies that make underwater sound monitoring more accessible. Walruses are among the more vocal pinnipeds, and their calls play important roles in maintaining social bonds, establishing dominance, and coordinating mother-pup reunions on crowded haul-outs.

A spectrogram is essentially a visual representation of sound: time runs along the x-axis, frequency along the y-axis, and amplitude is shown by color intensity. Learning to read spectrograms is a fundamental skill in bioacoustics, applicable to work with everything from songbirds to cetaceans. Once you can look at a spectrogram and instantly recognize the difference between a harmonic call and a broadband noise burst, you've got a tool you'll use for the rest of your career.

Pinniped vocal communication remains understudied compared to cetaceans, which means there are genuine open questions here. The functional significance of many walrus call types is still debated in the literature, and careful observational work linking calls to contexts is exactly the kind of data that moves the field forward.