Although the microstructures of Type-I collagen in bone and F-keratin in avian feathers are very different, their plastic behaviour is similar. In both plasticity is thermally activated, with the activation enthalpy H = 1.1 eV in bone and 1.75 eV in feather. The activation volumes are v = 0.6 nm3in bone and v = 0.83 nm3in feather. This indicates that the rate controlling process in both is the breaking of electrostatic bonds.