No. 29: Sep-Oct 1993
Many species of birds show considerable variation in size, shape, and coloration in various parts of their ranges. Hithertofore, such geographical variations had been considered to be genetically controlled; that is, the genes also varied with the geography. But experiments in which the eggs of redwinged blackbirds were interchanged between nests in northern and southern Florida and also between Colorado and Minnesota seem to show that the environment is more important than genetic endowment.
In the redwinged blackbird, the bill size and shape and body weight of the transplanted birds (after hatching, of course) were characteristic of the locale in which they were raised rather than that where the eggs were laid.
(James, Frances C.; "Environmental Component of Morphological Differentiation in Birds," Science, 221:184, 1983.)