Proximal mechanisms for sound production in male Pacific walruses

The songs of male walruses during the breeding season have been noted to have some of the most unusual characteristics that have been observed among mammalian sounds. In contrast to the more guttural vocalizations of most other carnivores, their acoustic displays have impulsive and metallic features more similar to those found in industrial work places than in nature. The patterned knocks and bells that comprise male songs are not thought to be true vocalizations, but rather, sounds produced with structures other than the vocal tract and larynx. To determine how male walruses produce and emit impulsive and metallic signals, we conducted a series of in situ studies with two captive adult male Pacific walruses that were trained for voluntary participation in bioacoustic research. Through a combination of observational, acoustic, endoscopic, and ultrasonic methods, we confirmed the probable anatomical origins of knocking and bell sounds and gained a mechanistic understanding of how these sounds are generated within the body and transmitted to the environment. These pathways are illustrated with acoustic and video data and considered with respect to the unique biology of this species.