A graphical method for dating chicks using bivariate body measurements

Abstract
Jones et al. (2005, J. Agric. Biol. and Env. Stat., 10: 306-320) developed a bivariate, nonlinear, mixed, growth-curve model, in order to estimate the ages of tern chicks from paired measurements of wing length and body weight. They found that age estimates obtained from a pair of measurements were much more precise than using either one alone. We present a graphical method for obtaining approximate answers to the same problem, but invoking fewer modelling assumptions. We obtain fiducial limits for dates by assessing whether pairs of measurements fall within confidence ellipses in the predicted morphological spaces of chicks of given ages. However, our conclusions differ markedly from those obtained by Jones et al.: we found that precisions of date estimates obtained using wing lengths alone were similar to those using both body measures.
Year
2009
Category
Refereed journal
Output Tags
SG 2006-2011 WP 3.6 Species, Habitats and Ecosystems