Growth of duck bills

We analyzed growth in length and width of bill in Mallards (Anas platyrhync hos), Pekin (Anas platyrhynchos f. domestica) and Muscovy (Cairina moschata f. domestica) Ducks with growth curve analysis. Bill growth is characteriz ed by a relatively high proportion of growth realized prehatching and early posthatching points of inflection. Individual variability of bill measurem ents limits its value for estimating age. Bill width is already further dev eloped at hatching than length, a difference that is maintained throughout the posthatching period. Consequently, bill width has a lower allometric ex ponent than length. This delay in development of length vs. width probably reflects overall development of the skull. Skull development is in turn clo sely related to brain growth, thus bill dimensions correlated with brain ma ss with coefficients of determination of ca. 0.9.