THE YOUNGS-MODULUS OF FEATHER KERATIN

The flexural stiffness of the rachis varies along the length of a prim ary feather, between primaries and between species; the possible contr ibution of variations in the longitudinal Young's modulus of feather k eratin to this was assessed. Tensile tests on compact keratin from eig ht species of birds belonging to different orders showed similar modul i (mean E=2.50 GPa) in all species apart from the grey heron (E=1.78 G Pa). No significant differences were seen in the modulus of keratin fr om primaries 7-10 in any species. There was a systematic increase in t he modulus distally along the length of the rachis from swan primary f eathers. Dynamic bending tests on swan primary feather rachises also s howed that the longitudinal elastic modulus increases with increasing frequency of bending over the range 0.1-10 Hz and decreases monotonica lly with increasing temperature over the range -50 to +50 degrees C. T he position-, frequency- and temperature-dependent variations in the m odulus are, however, relatively small, It is concluded that, in the sp ecies studied, the flexural stiffness of the whole rachis is principal ly controlled by its cross-sectional morphology rather than by the mat erial properties of the keratin.