What causes the sound of a seal barking?
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Causes of Seal Barking: Insights from Research
Vocalization Patterns in Seals
High-Amplitude Vocalizations in Northern Elephant Seals
Male northern elephant seals (Mirounga angustirostris) produce loud, stereotyped calls during the breeding season. These calls are characterized by high amplitude and serve as rigid signals to convey individual identity within noisy breeding colonies. The calls are measured to have mean source levels ranging from 98 to 131 dB, depending on the metric used. Interestingly, these seals do not adjust their call amplitude in response to higher background noise levels, indicating a lack of the Lombard effect, which is common in many other animals.
Australian Fur Seal Vocal Repertoire
Australian fur seals (Arctocephalus pusillus doriferus) exhibit a diverse vocal repertoire during the breeding season, including barks, guttural threats, and submissive calls. The male bark call, in particular, varies in rate depending on the context: it is slower when males are stationary and advertising their territorial status and faster during confrontations or when herding females. This variation in call rate suggests that the bark serves multiple social functions, from territory advertisement to aggressive interactions.
Underwater Vocalizations in Ringed Seals
Ringed seals (Phoca hispida) also produce vocalizations, although these are primarily underwater and include high- and low-pitched barks, yelps, and chirps. These sounds likely facilitate communication and social organization among individuals.
Environmental and Social Influences on Seal Barking
Directionality and Receiver Behavior in Northern Elephant Seals
The directionality of male northern elephant seal threat calls significantly influences receiver behavior. These calls are particularly directional at frequencies above 1 kHz, and the responses of other males in reproductive competition are affected by the directionality of the calls. This suggests that the orientation of the signaler plays a crucial role in the effectiveness of the communication.
Impact of Motor Boat Noise on Australian Fur Seals
Australian fur seals show significant behavioral responses to motor boat noise, with increased aggression and alertness at higher noise levels (75-85 dB). The seals also exhibit plasticity in their vocal responses, with barks becoming faster as the boat noise gets louder. This indicates that environmental noise can influence the vocal behavior of seals, potentially affecting their communication and social interactions.
Conclusion
Seal barking is influenced by a combination of social and environmental factors. In northern elephant seals, high-amplitude vocalizations serve as rigid signals for individual identification, while in Australian fur seals, the rate of barking varies with social context. Environmental noise, such as motor boat sounds, can also impact seal vocalizations, leading to changes in behavior and communication patterns. Understanding these vocalization patterns and their underlying causes is crucial for the conservation and management of seal populations.
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