Comparative mechanics of bill, claw, and feather keratin in the common starling Sturnus vulgaris

The Vickers microhardness of non-melanic keratin was measured from the bills, claws and outer primaries of Common Starlings Sturnus vulgaris. Highly significant differences in hardness were found between all three keratin types. Bill keratin was the hardest and feather keratin the least hard; the relative molecular weight of the different keratin types may explain these differences. Indentation hardness can be used as a measure of the competence of a material to resist abrasive wear so it is likely that the three keratin types differ in their competence at resisting abrasive wear.