Abstract
We propose to study the mechanics of avian vocalisation. A biomechanical model is being developed that includes the following elements.
1. The flow and pressure distribution of the air inside and outside the vocalisation apparatus is calculated using computational fluid dynamics (CFD).
2. Flow induced vibrations of the principal membranes and labia in the syrinx (the vocal organ) are calculated from their measured geometry and mechanical properties.
3. The influence of syringeal muscles on the vibrational modes of the membranes will be simulated by including dynamic muscle models.
Such an integrated model is essential for studies of functional morphology, neuromuscular control, and behaviour. The recently developed elements (1) and (2) of the model will be improved and element (3) is a required extension. Experiments will be done to obtain values for the input parameters and to test model predictions. Input parameters to be measured include dimensions and material properties of the vocalisation system. The validity of the CFD calculations will be separately tested with a mechanical analogue of the birds' vocalisation apparatus with a simplified geometry. In this 'artificial bird', high accuracy measurements can be made. Flow fields will be measured with laser sheet particle image velocimetry, while membrane vibrations will be measured with a laser-vibrometer and high-speed film or video. Secondly, measurements of sound, flow and pressure will be made in some selected bird species (e.g. chickens, pigeons, doves and parrots). The model will be tested also against experimental data of the acoustic power level, wave form and frequency spectrum of avian song.
Finally, model predictions and tests will be made for birds singing in a mixture of oxygen and helium (with a lower density than air). |
