What causes the sound of a walrus bellowing?
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Causes of the Sound of a Walrus Bellowing
Walrus Vocal Repertoire and Sound Production Mechanisms
Walruses are known for their complex and diverse vocalizations, particularly during the breeding season. The primary sounds produced by male walruses include rhythmic "knocks" and metallic "bells," which are part of their underwater songs . These sounds serve as a means of communication and display during mating rituals, conveying physical fitness to potential mates and rivals.
Knocking Sounds: Forehead Movements and Testosterone Levels
The knocking sounds are produced through visible impulsive movements of the forehead. These knocks can be emitted as single pulses or in sequences of doublets and triplets, typically repeated at rates of 0.8 to 1.2 knocks per second. The production of these sounds is loud, with source levels averaging 186 dB and frequencies exceeding 24 kHz. Interestingly, the persistence of these knocking displays is strongly correlated with the male walrus's seasonal testosterone levels, indicating a hormonal influence on sound production.
Clapping Sounds: Fore Flipper Collision and Cavitation
In addition to knocking, male walruses can produce intense, rhythmic sounds through a non-vocal pathway involving the deliberate collision of their fore flippers. This clapping behavior generates sounds via cavitation, with each forceful clap producing acoustic impulses that exceed 200 dB. Although this clapping behavior has not been documented in wild walruses, it has been observed in captive individuals, suggesting it may be a common but underreported sound production mechanism among mature males.
Acoustic Monitoring and Sound Localization
Extended acoustic monitoring programs have identified walrus knocks and bell-like calls across large regions, such as the Chukchi Sea. These studies utilize seabed-mounted acoustic recorders to track walrus movements and behaviors based on their vocalizations. The average knock production rate has been recorded at 59 to 75 knocks per minute, with source levels around 177.6 dB. This monitoring helps in understanding the spatial and temporal distribution of walrus sounds and their behavioral contexts .
Novel Sound Production and Learning
Walruses exhibit a high degree of plasticity in their sound emissions, capable of producing novel sounds through contingency learning. In captivity, walruses have been trained to vary their sound emissions by reinforcing new and different sounds. This ability to learn and produce novel sounds suggests that walruses can adapt their vocalizations based on environmental and social cues. Both male and female walruses have been observed to spontaneously emit knocks and soft bells, components of the songs typically produced by males during the breeding season.
Conclusion
The sound of a walrus bellowing is a complex interplay of biological, hormonal, and learned behaviors. The primary sounds, including knocks and bells, are produced through specific physical movements and are influenced by testosterone levels. Additionally, walruses can produce intense clapping sounds through fore flipper collisions, a behavior observed in captivity. Acoustic monitoring and contingency learning studies further reveal the adaptability and diversity of walrus vocalizations, highlighting their sophisticated communication system.
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