Corn Crake (Crex crex) Science Article 1
A comparison of Corncrakes Crex crex of known age showed that the tips of the secondary remiges were, on average, more pointed for birds with remiges grown in the hatching year (HY) than for older adults with remiges grown after the hatching year (AHY; Green et al 2001). It might be that this difference is due to an age-related change in the shape of secondaries grown by the same bird. The magnitude of the change would suggest that an alternative explanation of the age difference, that juveniles with less pointed secondaries are more likely to survive to become adults, seems less plausible. […].
Rhys E. Green, Ringing & Migration (2004) 22, 83-84