Terrestrial Carnivore Sounds with Repeated Rapid Alternation of Two Structurally Different Components: an Indication of Complex Sound Production Mechanisms in Mammals?

Acoustic signals of several species from different families of the terrestrial Carnivora (Mammalia) are described and discussed in detail. All show a rapid and regular repetitive alternation between two structurally different component sound elements. It is argued that this general structural feature is indicative of different morphological structures or mechanisms in the larynx or supralaryngeal vocal tract, contributing to sound production or modification in a temporally coordinated way. A few examples are listed of acoustic signals in the aquatic Carnivora and mammalian orders other than the Carnivora showing a similar general structural pattern. Several of the relevant acoustic signals mentioned include sound production by the laryngeal source but morphological structures in the supralaryngeal vocal tract are likely to generate additional components in some of these. Sounds also exist with two different structural components alternating without contribution of the laryngeal source to sound generation. In nearly all the examples given, knowledge as to the definite nature and mode of action of these structures and as to their temporal coordination is only fragmentary at best. It is important to clarify the respective share of each morphological structure and physiological mechanism contributing to sound production and modification in order to characterize and classify an animal acoustic signal and when studying specific signals in a comparative phylogenetic context.