Figure 7. SEM. Primary flight feather of Polihierax semitorquatus. Cortex. Section longitudinally peeled at ~mid-rachis length. Right side.

(a) The partial stripping of the SBFs by the peeling process shows in situ the dynamic nature of SBF cohesion and compaction and how bonding is achieved by just a thin layer of matrix. On the right, two SBFs have bonded almost into one. Hemi-circles define thickness of some SBFs. (b) Presence of a small infestation of fungi. The matrix is still intact and un-degraded showing that there is little additional thickness compared to a degraded SBF (c). (c) Close by (to the left of (a) fungi have completely stripped a SBF of its matrix, showing the typical structure.