Effects of Nestling Diet on Growth and Adult Size of Zebra Finches (Poephila guttata)

Abstract Manipulation of the diet of Zebra Finch (Poephila guttata) nestlings in the laboratory showed that a low-quality diet reduced growth rates of nine external morphological characters, while a high-quality diet increased growth rates. The growth of plumage characters was least affected by diet, while growth rates of tarsus and mass were most affected. The treatments also produced differences in the adult size of experimental birds, differences not evident in either their parents or their own offspring. Diet quality had the strongest impact on adult mass and tarsus length, while plumage and beak measurements were less affected. Analysis using principal components and character ratios showed that the shape of experimental birds was affected by the experimental diets, but to a minor extent compared with changes in overall size. Significant shape changes involved ratios between fast- and slow-growing characters. The ratios of characters that grow at similar, slow rates (e.g. beak shape) were not affected by the diets. Environmental sources of morphological variation should not be neglected in studies of phenotypic variation in birds.