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In general, a bird can be considered as a system to which energy, in the form of food, is supplied. The bird uses this energy for various purposes including flight and body temperature regulation. Knowledge of how the energy is used by the bird in flight gives insight into its efficiency. This knowledge, combined with insight into migration behaviour and the energy conversion processes within a bird promises understanding of relationships between available food during a particular season and a bird’s range of migration. This is of particular interest due to fluctuating climate and a bird’s ability to transport disease.

Knowledge of the energy used by the bird in flight necessitates investigation into the interaction between the bird and the air in which it flies. There are many differences between a bird’s wing and the wings of an airplane (for example) that must be considered. These differences include the fact that a bird’s wing moves and flexes relative to its body. Also, a bird’s wing operates in a Reynolds number range in which viscosity effects are noticeable and surface roughness plays a relatively large role in the boundary layer behaviour and the generation of turbulence. In addition to the various feather types that exist on the wing, surface lubrication must also be considered. Migrating bird species, including the yellow throated sparrow, coat their bill with preen wax and rub it on their feathers. It is possible that, like other animals, birds may lubricate their bodies to reduce skin friction drag.

Due to the complexity of the movement as well as the details of the boundaries, the use of computational fluid dynamics is limited in this particular field. Also, an analytical approach can only provide limited theories since many assumptions must be made before the problem becomes solvable. The research shall therefore be conducted using High Speed Particle Image Velocimetry (PIV). Generally speaking, PIV reconstructs a velocity field by considering pairs of images showing particles suspended in the flow. Although particles are distributed homogeneously, the use of a laser sheet ensures only desired regions of the flow are measured. The displacement of particles in the flow and the time between the image captures allows the calculation of a velocity field.

In this particular study, several velocity fields shall be taken in orthogonal orientations relative to the airflow approaching the bird. The use of the High Speed PIV and two cameras operating simultaneously will allow the measurement of planes of three-component velocity vectors. At this stage of investigation, eight stationary models of the bird at different phases in the wing beat cycle are considered. Although the overall flow field will differ greatly between a stationary wind tunnel model and an actual sparrow, insight will be gained into what features of the wing (feathers, edges, etc.) are of interest before the complexity of wing motion is added. Also, the stationary models provide an opportunity to compare the models with and without preen wax and determine the possible drag reducing mechanism.

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