MECHANICAL PROPERTIES OF BIRD FEATHERS - Influence of UV-Radiation and Mechanical Fatigue

When birds move around in their natural environment the feathers on the wings are exposed to various factors that reduce their performance, such as UV-radiation, mechanical wearing and bacteria. In time the feathers get worn out and are replaced. This usually happens once a year by a process called moult. Some bird species differs from this pattern and moult twice a year. This behavior may have influence on the mechanical properties of the feathers, and the feathers may respond differently to different kinds of exposure such as UV-radiation and mechanical wearing. Three experiments were performed on feathers from two different moulting bird species. A UV-radiation-, mechanical wearand a combination of the two on the Chiffchaff Phylloscopus collybita, which moult once a year, and the Willow Warbler Phylloscopus trochilus, which moult twice a year. To investigate the influence of these experiments on the mechanical properties of feathers a bending stiffness test was performed after each exposure. A finite element study was made to investigate the basic mechanical behavior of the feather shaft. A comparison between the FE-simulation and the experiment showed a good agreement. The results from the experiments showed that for shorter exposure times of UVradiation the bending stiffness increases then to decrease below the original stiffness value for longer UV-exposures. The mechanical wearing was found to constantly decrease the bending stiffness. The conclusions from the experiments are that differences between the two bird species exist. From the UV-experiment very small differences in bending stiffness were found. From the mechanical wear-experiment and the mechanical wear part from the combined experiment, larger differences were found, in which the bending stiffness decreases more rapidly for the Willow Warbler than for the Chiffchaff. In the combined experiment the UV-radiation did not increase the bending stiffness as was observed in the single UV-experiment. The combined experiment also made the bending stiffness to decrease more rapidly for the mechanical wearing than was observed in the single mechanical wear-experiment.