Estimating the age of Corncrake Crex crex chicks from body weight and the development of primary

Two methods for ageing Corncrake Crex crex chicks are described. Data on the body weight of chicks of known age, from broods of radio-tagged females, were used to produce a formula for determining the age of chicks of unknown age. This method was, however, prone to error for chicks older than about 22 days after hatching. An alternative method, based on the ratio of the length of the waxy sheath on a primary feather to the maximum chord wing length, was developed using measurements of captive-bred chicks of known age. This method performed well for chicks aged 22-45 days old, but required testing on wild chicks before application because of possible effects of captive rearing. Estimates of the age of wild chicks from both weight and primary development indicate that the two methods gave similar results and, hence, that the latter method was useful for chicks older than 22 days.

Rhys E. Green, Ringing & Migration (2005) 22, 139-144