PDF - Wallace Online

vi A THEORY OF BIRDS' NESTS 135formed chiefly of fir-twigs and lichens. Now the delicategray and ashy and purplish hues of the head and back, togetherwith the yellow of the wings and tail, are tints thatexactly harmonise with the colours of fir leaves, bark, andlichens, while the brilliant red wax tips exactly represent thecrimson fructification of the common lichen, Cladonia coccifera.When sitting on its nest, therefore, the female birdwill exhibit no colours that are not common to the materialsby which it is surrounded and the several tints are distributedin about the same proportions as they occur in nature.;At a short distance the bird would be undistinguishable fromthe nest it is sitting on, or from a natural clump of lichens,and will thus be completely protected.I think I have now noticed all exceptions of any importanceto the law of dependence of sexual colour on modification.It will be seen that they are very few in number, comparedwith those which support the generalisation ;and in severalcases there are circumstances in the habits or structure of thespecies that sufficiently explain them. It is remarkable alsothat I have found scarcely any positive exceptions that is,cases of very brilliant or conspicuous female birds in whichthe nest was not concealed. Much less can there be shownany group of birds in which the females are all of decidedlyconspicuous colours on the upper surface, and yet sit in opennests. The many cases in which birds of dull colours in bothsexes make domed or concealed nests do not, of course, affectthis theory one way or the other since its ; purpose is onlyto account for the fact that brilliant females of brilliantmales are always found to have covered or hidden nests, whileobscure females of brilliant males almost always have open andexposed nests. The fact that all classes of nests occur withbirds which are dull coloured in both sexes merely showsthat these dull colours serve to protectthe parents at othertimes than when sitting on the nest, the structure of which isdetermined by the requirements of the offspring.If the views here advocated are correct, as to the variousinfluences that have determined the specialities of every bird'snest, and the generalcoloration of female birds, with theiraction and reaction on each other, we can hardly expect tofind evidence more complete than that here set forth. Nature