The walrus, Odobenus rosmarus, is a massive marine mammal of the Arctic, recognized by its prominent tusks and thick, wrinkled hide. This pinniped possesses a complex underwater communication system. Walruses are highly social animals that rely on an extensive array of sounds to navigate their icy environment and maintain group cohesion, ranging from low-frequency rumbles to delicate, musical tones.
The Walrus Vocal Repertoire
Walruses are among the most vocal pinnipeds, producing airborne and waterborne sounds. Their repertoire includes growls, barks, snorts, and rasps, which are mostly used when the animals are hauled out on land or ice. Underwater, where sound travels farther and faster, they use vocalizations including clicks, taps, and knocks. The sound often described as a “whistle” is typically a soft, high-frequency vocalization used for close-range social contact while swimming.
The most distinctive and studied underwater sound is the metallic, bell-like call, sometimes referred to as a “ting” or click train. This bell sound is a clear, long-duration pulse that projects powerfully through the water. This unique acoustic signal is a fundamental component of the elaborate, rhythmic sound sequences produced by males. These complex patterns of sound can persist for long periods.
The Unique Mechanism of Walrus Sound Production
Walruses have evolved specialized anatomical structures that enable them to generate sounds underwater without losing air. Unlike the sounds produced by their vocal cords, the metallic bell-like calls originate from air sacs known as pharyngeal pouches. These two large, inflatable pouches extend from the pharynx in the throat and can hold several gallons of air.
The walrus controls the airflow within these sacs, manipulating the air to create the acoustic energy that results in the metallic, resonating tone. This allows the walrus to produce loud, clear sounds at depth without the typical bubbling or air loss that would occur with laryngeal vocalization. The ability to manipulate air in this way enables them to generate a wide range of unique sounds.
Context and Meaning in Walrus Communication
Walrus vocalizations are linked to specific social and behavioral contexts, primarily during the breeding season. Male walruses use their intricate acoustic displays, including the bell-like calls and rhythmic knocks, as a form of competitive courtship. These elaborate “songs” are among the longest and most complex continuous reproductive displays known among mammals. The songs are thought to convey a male’s physical fitness and endurance to potential mates and rivals, sometimes being heard up to 16 km away.
Sound is a tool for daily survival and social maintenance within the herd. When walruses are swimming in groups, soft whistles are used to maintain contact, ensuring that individuals do not become separated, especially in low-visibility or dark Arctic waters. On land or ice, where they gather in massive groups, they use grunts and snorts as a form of background chatter to reinforce social cohesion and coordinate the movements of the large assemblage.
Acoustic recognition is also involved in the bond between mother and calf. Mother walruses and their young rely on vocal cues to identify each other, which is crucial in the crowded environment of a haul-out or when separated underwater. Mothers use soft bellows and grunts to communicate affection and confirm the location of their calf, a bond that can persist for several years after the calf is weaned. In contrast, adults engaged in dominance conflicts may use louder, more aggressive sounds like snorts, coughs, or roars to establish hierarchy without resorting to physical confrontation.
Studying Walrus Sounds and Conservation
Scientists study walrus communication primarily through passive acoustic monitoring, using hydrophones deployed in Arctic waters. This technology allows researchers to record and analyze the underwater soundscape over extended periods. By analyzing the patterns of bell calls, knocks, and whistles, researchers can monitor population health, track migration routes, and identify important breeding and foraging grounds.
Understanding walrus acoustics is becoming increasingly important for conservation efforts due to the increase in human activity. The noise generated by ship traffic, drilling, and seismic surveys introduces low-frequency sounds that can travel long distances. This human-made noise can mask the walruses’ vocalizations, a phenomenon known as acoustic masking, which impairs their ability to communicate. Auditory masking is a serious threat, particularly to young calves, as it can prevent them from reuniting with their mothers, thereby impacting their survival rate.