Vocal tract articulation revisited: the case of the monk parakeet

Abstract

SUMMARYBirdsong and human speech share many features with respect to vocal learning and development. However, the vocal production mechanisms have long been considered to be distinct. The vocal organ of songbirds is more complex than the human larynx, leading to the hypothesis that vocal variation in birdsong originates mainly at the sound source, while in humans it is primarily due to vocal tract filtering. However, several recent studies have indicated the importance of vocal tract articulators such as the beak and oropharyngeal-esophageal cavity. In contrast to most other bird groups, parrots have a prominent tongue, raising the possibility that tongue movements may also be of significant importance in vocal production in parrots, but evidence is rare and observations often anecdotal. In the current study we used X-ray cinematographic imaging of naturally vocalizing monk parakeets (Myiopsitta monachus) to assess which articulators are possibly involved in vocal tract filtering in this species. We observed prominent tongue height changes, beak opening movements and tracheal length changes, which suggests that all of these components play an important role in modulating vocal tract resonance. Moreover, the observation of tracheal shortening as a vocal articulator in live birds has to our knowledge not been described before. We also found strong positive correlations between beak opening and amplitude as well as changes in tongue height and amplitude in several types of vocalization. Our results suggest considerable differences between parrot and songbird vocal production while at the same time the parrotʼs vocal articulation might more closely resemble human speech production in the sense that both make extensive use of the tongue as a vocal articulator. Supplementary material available online at

Factors shaping the ontogeny of vocal signals in a wild parrot

“…Short-duration calls are consistent with the fact that air cavities and respiratory organs were likely still small and undergoing substantial growth during this period (Vleck and Bucher, 1998). High frequencies are synonymous with short wavelengths of sound and are predicted from the resonant properties of small vocal tracts (Podos, 1996;Brittan-Powell et al, 1997;Hoese et al, 2000;Suthers and Zollinger, 2004;Beckers et al, 2004;Bradbury and Vehrencamp, 2011;Ohms et al, 2012). Broadband noise has been…”

“…The latter characteristic suggests an advantage to calling while flapping. Because downstroke phases are often synchronized with expiratory phases (Tucker, 1968;Boggs, 1997;Tobalske and Dial, 1994), and vocal production requires a build-up of positive expiratory pressure at the sub-syringeal aperture (Suthers, 1997;Cooper and Goller, 2004;Ohms et al, 2012), contact call emission may be more economical during flapping phases and less so during non-flapping phases when inspiration is likely more economical. In support of this explanation, nestling call durations showed an abrupt decrease shortly after they began using wings to aid locomotor displacements inside the nest cavity.…”

Lingual articulation in songbirds

“…A high-low placement of the tongue changes the frequency of the first formant, and a front-back placement changes the frequency of the second formant. Although little is known about their importance in avian communication, formants or harmonic-rich formant-like structures are also observed in the vocalizations of various bird species, including zebra finches (Ohms et al, 2010), mynah birds (Klatt and Stefanski, 1974), African gray parrots (Pepperberg, 2010) and monk parakeets (Beckers et al, 2004;Ohms et al, 2012). The ability of mynah birds and parrots to modify formants contributes to their ability to imitate human speech, although the production mechanism may not be identical to that found in humans.…”

“…In an experiment in which the syrinx of a euthanized monk parakeet was replaced with a speaker, Beckers et al (2004) found that artificially manipulating front-back tongue placement caused changes in formant frequency and amplitude, and manipulating high-low placement caused changes in amplitude. Ohms et al (2012) used Xray cineradiography to measure tongue height in naturally vocalizing monk parakeets. Changes in tongue height were observed during the production of various natural call notes.…”

Coos, booms, and hoots: The evolution of closed‐mouth vocal behavior in birds

“…), in the open‐mouth vocalizing species monk parakeet ( Myiopsitta monachus ; Ohms et al. ), or in the open‐mouth vocalizations of songbirds (Riede and Suthers ; Ohms et al. ; Riede and Goller ; Riede et al.…”