nydus/Contributions to the Theory of Natural SelectionPublic
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VII. A THEORY OF BIRDS’ NESTS; Showing the relation of certain differences of colour in Female Birds, to their mode of Nidification.
Grallina Australis. This Australian bird is of strongly contrasted
black and white colours. The sexes are exactly alike, and it builds an
open clay nest in an exposed situation on a tree. This appears to be a
most striking exception, but I am by no means sure that it is so. We
require to know what tree it usually builds on, the colour of the bark
or of the lichens that grow upon it, the tints of the ground, or of
other surrounding objects, before we can say that the bird, when sitting
on its nest, is really conspicuous. It has been remarked that small
patches of white and black blend at a short distance to form grey, one
of the commonest tints of natural objects.
Sunbirds (Nectarineidæ). In these beautiful little birds the males only are adorned with brilliant colours, the females being quite plain, yet they build covered nests in all the cases in which the nidification is known. This is a negative rather than a positive exception to the rule, since there may be other causes besides the