An Hypothesis concerning the Relationship of Syringeal Structure to Vocal Abilities

Abstract

Neither the possession of large vocabularies or repertoires nor the ability to learn phonations can be precisely correlated with the structural complexity of a syrinx. Hence, some recent investigators have suggested that avian vocal plasticity arises solely from a neurological shift. A simple syrinx, i.e. one with only extrinsic musculature, is subject to certain constraints, however. Its configuration changes as a unit, and the factors responsible for modulating sounds cannot be independently varied. Thus, the temporal characteristics of sound patterns can be varied easily, but rapid juxtaposition of different modulatory patterns is difficult. Intrinsic musculature permits isolation and independent control of syringeal components and thereby simplifies control of modulations. Syringeal complexity may not be an adaptation (i.e. did not evolve under selection) for plastic vocal behavior, but it is permissive of and probably prerequisite for such behavior.

The songbird syrinx morphome: a three-dimensional, high-resolution, interactive morphological map of the zebra finch vocal organ

“…Compared with the huge variation in syringeal morphologies found in non-songbirds, the morphology of the songbird syrinx is quite conserved [16,19,20]. Gaunt previously proposed that more elaborate intrinsic muscles in songbirds allowed for independent control of song parameters [20].…”

“…Gaunt previously proposed that more elaborate intrinsic muscles in songbirds allowed for independent control of song parameters [20]. Field recordings [91], excised preparations [92], mechanical models [93,94] and numerical models of sound production in non-songbirds, such as ringdoves ( Streptopelia risoria ) [95], and sub-oscines (Passeriformes: Tyranni), such as the great kiskadee ( Pitangus sulphuratus ) [96], show that sound amplitude and frequency are often coupled to some degree, thereby severely limiting the potential repertoire of syllables that can be produced physically.…”

“…For over 200 years, morphologists and systematists have used the cross-species diversity of syringeal anatomy to classify avian taxa. The syrinx of the more than 4,000 songbird (Aves: Passeriformes: Passeri) species exhibits substantial anatomical variation [18,19], but is morphologically conserved compared with other avian taxa [16,20]. Previous work has led to insights on syringeal biomechanics and song physiology, but experimental limitations have focused research primarily on larger songbird species [21-28].…”

Integrative physiology of fundamental frequency control in birds

“…The syrinx of oscine songbirds therefore appears to have gained an additional degree of freedom in F 0 control compared to the vocal organs of non-passeriform groups and perhaps even suboscine groups. This added control mechanism is likely to have contributed to the spectral diversity found in oscine vocal repertoires (Table 1; see also Gaunt, 1983, 1987). …”

Peripheral mechanisms for vocal production in birds – differences and similarities to human speech and singing

“…The morphology of the avian syrinx varies substantially between different taxa and shows a high degree of specialization in oscine songbirds (e.g., King, 1989), although little of this morphological variability can be linked to specific features of a species’ vocal repertoire (Gaunt, 1983). Modified cartilages form a cylinder-like structure, the tympanum.…”