Pressure and air flow during distress calls of the starling, <i>Sturnus vulgaris</i> (Aves;Passeriformes)

Abstract

Abstract Present hypotheses for the operation of the syringeal mechanism can be reduced to two models differing in whether closure of the syringeal bore is attributed to a pressure differential on either side of the vibrating membrane or to contraction of the syringeal musculature. Paucity of data, especially for songbirds, concerning the behavior of ventilated air during calling hinders application of either of the models to specific portions of the repertoire of any bird. Internal and tracheal pressures and air flow are recorded during distress calls of the starling. Air sac pressures soar, often to more than 20 cm H 2 0 ( × 40 normal respiratory amplitudes), while tracheal pressures are the same or lower than during respiration. A distress call lasts twice as long as a normal exhala tion, but flow is reduced and tidal volume increases only slightly. Seemingly, the syringeal valve can regulate flow across a large, sustained pressure differential. The inability of birds to vocalize when the interclavicular air sac is ruptured is more easily explained by an alteration of flow to bypass a closed, pressure independent valve than a necessity for a high pressure surrounding the syrinx during vocalization. These studies suggest that reduction of the syringeal lumen in songbirds is at least partially dependent on active con‐ striction rather than a passive flutter valve. The possible nature and selective implications of such a mechanism are discussed.