Growth and allometry of external morphology in Darwin's finches (Geospiza) on Isla Daphne Major, Galapagos

Abstract

Seven widely used avian external morphological measurements were examined, mainly in Geospiza fortis and G. scandens on Isla Daphne Major, Galapagos. Geospiza grow more slowly than other “finches”, and smaller Geospiza species grow relatively more slowly than larger Geospiza. Weight, wing chord and tarsus grow quickly, while bill characters grow more slowly. This pattern of relative growth (dynamic allometry) is reversed in the static allometry of adults, where bill characters, particularly bill depth in G. fortis, display strong, positive allometry with respect to weight, wing and tarsus. Static allometric patterns help explain differences in the size, shape and relative variability of different characters in adults, as well as the results of multivariate analyses such as principal components or canonical variates. Several different multivariate techniques arrange five Geospiza populations in a consistent two‐dimensional morphological space, with a major axis of overall “body‐size”, and a minor axi of “bill‐pointedeness”. An alternative analysis of dynamic and static allometry is also provided, based on multivariate techniques.