Growth of duck bills

Abstract

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